bookmarks: when @ bookmark diverges, don't double the @ sign (BC)

This changeset treats the bookmark "@" as a special case for the naming of
divergent bookmarks, as per the tables below.  For the <no alias> case, the
actual suffix will vary, depending on what suffixes are already in use.

Before:
Bookmark | Remote     | Divergent Bookmark
--------------------------------------
foo      | bar        | foo@bar
foo      | <no alias> | foo@1
@        | bar        | @@bar
@        | <no alias> | @@1

After:
Bookmark | Remote     | Divergent Bookmark
--------------------------------------
foo      | bar        | foo@bar
foo      | <no alias> | foo@1
@        | bar        | @bar
@        | <no alias> | @1

This case is likely to be more common now that 92980a8dfdfe has made the "@"
bookmark have special meaning to clone.

The change in behavior was discussed on the mailing list in the thread below:
http://markmail.org/thread/rwedgxp7le5j2h2f

mercurial/bookmarks.py

@@ -214,16 +214,20 b' def updatefromremote(ui, repo, remote, p'
                     changed = True
                     ui.status(_("updating bookmark %s\n") % k)
                 else:
+                    if k == '@':
+                        kd = ''
+                    else:
+                        kd = k
                     # find a unique @ suffix
                     for x in range(1, 100):
-                        n = '%s@%d' % (k, x)
+                        n = '%s@%d' % (kd, x)
                         if n not in repo._bookmarks:
                             break
                     # try to use an @pathalias suffix
                     # if an @pathalias already exists, we overwrite (update) it
                     for p, u in ui.configitems("paths"):
                         if path == u:
-                            n = '%s@%s' % (k, p)
+                            n = '%s@%s' % (kd, p)
 
                     repo._bookmarks[n] = cr.node()
                     changed = True

tests/test-bookmarks-pushpull.t

@@ -111,8 +111,10 b' divergent bookmarks'
   $ echo c1 > f1
   $ hg ci -Am1
   adding f1
+  $ hg book -f @
   $ hg book -f X
   $ hg book
+     @                         1:0d2164f0ce0d
    * X                         1:0d2164f0ce0d
      Y                         0:4e3505fd9583
      Z                         1:0d2164f0ce0d
@@ -124,8 +126,10 b' divergent bookmarks'
   $ echo c2 > f2
   $ hg ci -Am2
   adding f2
+  $ hg book -f @
   $ hg book -f X
   $ hg book
+     @                         1:9b140be10808
    * X                         1:9b140be10808
      Y                         0:4e3505fd9583
      Z                         0:4e3505fd9583
@@ -141,8 +145,11 b' divergent bookmarks'
   added 1 changesets with 1 changes to 1 files (+1 heads)
   divergent bookmark X stored as X@foo
   updating bookmark Z
+  divergent bookmark @ stored as @foo
   (run 'hg heads' to see heads, 'hg merge' to merge)
   $ hg book
+     @                         1:9b140be10808
+     @foo                      2:0d2164f0ce0d
    * X                         1:9b140be10808
      X@foo                     2:0d2164f0ce0d
      Y                         0:4e3505fd9583
@@ -157,6 +164,7 b' divergent bookmarks'
   adding file changes
   added 1 changesets with 1 changes to 1 files (+1 heads)
   $ hg -R ../a book
+     @                         1:0d2164f0ce0d
    * X                         1:0d2164f0ce0d
      Y                         0:4e3505fd9583
      Z                         1:0d2164f0ce0d
@@ -177,6 +185,7 b' update a remote bookmark from a non-head'
   added 1 changesets with 1 changes to 1 files (+1 heads)
   updating bookmark Y
   $ hg -R ../a book
+     @                         1:0d2164f0ce0d
    * X                         1:0d2164f0ce0d
      Y                         3:f6fc62dde3c0
      Z                         1:0d2164f0ce0d
@@ -206,6 +215,7 b' diverging a remote bookmark fails'
   (did you forget to merge? use push -f to force)
   [255]
   $ hg -R ../a book
+     @                         1:0d2164f0ce0d
    * X                         1:0d2164f0ce0d
      Y                         3:f6fc62dde3c0
      Z                         1:0d2164f0ce0d
@@ -221,6 +231,7 b' Unrelated marker does not alter the deci'
   (did you forget to merge? use push -f to force)
   [255]
   $ hg -R ../a book
+     @                         1:0d2164f0ce0d
    * X                         1:0d2164f0ce0d
      Y                         3:f6fc62dde3c0
      Z                         1:0d2164f0ce0d
@@ -241,6 +252,7 b' Update to a successor works'
   remote: added 1 changesets with 1 changes to 1 files (+1 heads)
   updating bookmark Y
   $ hg -R ../a book
+     @                         1:0d2164f0ce0d
    * X                         1:0d2164f0ce0d
      Y                         4:4efff6d98829
      Z                         1:0d2164f0ce0d
@@ -263,11 +275,12 b' hgweb'
   namespaces	
   obsolete	
   $ hg debugpushkey http://localhost:$HGPORT/ bookmarks
+  @	9b140be1080824d768c5a4691a564088eede71f9
+  foo	0000000000000000000000000000000000000000
+  foobar	9b140be1080824d768c5a4691a564088eede71f9
   Y	4efff6d98829d9c824c621afd6e3f01865f5439f
-  foobar	9b140be1080824d768c5a4691a564088eede71f9
+  X	9b140be1080824d768c5a4691a564088eede71f9
   Z	0d2164f0ce0d8f1d6f94351eba04b794909be66c
-  foo	0000000000000000000000000000000000000000
-  X	9b140be1080824d768c5a4691a564088eede71f9
   $ hg out -B http://localhost:$HGPORT/
   comparing with http://localhost:$HGPORT/
   searching for changed bookmarks
@@ -289,10 +302,11 b' hgweb'
   $ hg pull -B Z http://localhost:$HGPORT/
   pulling from http://localhost:$HGPORT/
   no changes found
+  divergent bookmark @ stored as @1
+  adding remote bookmark foo
   adding remote bookmark foobar
+  divergent bookmark X stored as X@1
   adding remote bookmark Z
-  adding remote bookmark foo
-  divergent bookmark X stored as X@1
   importing bookmark Z
   $ hg clone http://localhost:$HGPORT/ cloned-bookmarks
   requesting all changes
@@ -303,6 +317,7 b' hgweb'
   updating to branch default
   2 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ hg -R cloned-bookmarks bookmarks
+     @                         1:9b140be10808
      X                         1:9b140be10808
      Y                         3:4efff6d98829
      Z                         2:0d2164f0ce0d