update: consider successor changesets when moving active bookmark

Previously, when an obsolete changeset was bookmarked, successor changesets were not considered
when moving the bookmark forward. Now that a bare update will move to the tip most of the
successor changesets, we also update the bookmark logic to allow the bookmark to move with this
update.

Tests have been updated and keep issue4015 covered as well.

mercurial/bookmarks.py

@@ -192,13 +192,12 b' def update(repo, parents, node):'
         return False
 
     if marks[cur] in parents:
-        old = repo[marks[cur]]
         new = repo[node]
         divs = [repo[b] for b in marks
                 if b.split('@', 1)[0] == cur.split('@', 1)[0]]
         anc = repo.changelog.ancestors([new.rev()])
         deletefrom = [b.node() for b in divs if b.rev() in anc or b == new]
-        if old.descendant(new):
+        if validdest(repo, repo[marks[cur]], new):
             marks[cur] = new.node()
             update = True
 

tests/test-update-branches.t

@@ -229,13 +229,16 b' the bookmark (issue4015)'
   $ hg bookmarks
    * bm                        5:ff252e8273df
 
-Test that 4 is detected as the no-argument destination from 3
+Test that 4 is detected as the no-argument destination from 3 and also moves
+the bookmark with it
   $ hg up --quiet 0          # we should be able to update to 3 directly
   $ hg up --quiet --hidden 3 # but not implemented yet.
+  $ hg book -f bm
   $ hg up
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  $ hg id
-  d047485b3896+ (b1)
+  updating bookmark bm
+  $ hg book
+   * bm                        4:d047485b3896
 
 Test that 5 is detected as a valid destination from 1
   $ hg up --quiet 0          # we should be able to update to 3 directly