linkrev: also adjust linkrev when bootstrapping 'follow' revset

The follow revset (used by `hg log --follow`) now uses the new 'introrev'
method to bootstrap its traversal. This catches issues from linkrev-shadowing of
the changesets introducing the version of a file in source changeset.

A new test has been added to display pathological cases.

Another test is affected because it was meant to test this behavior but actually
failed to do so for half of the output. The output are now similar.

mercurial/revset.py

@@ -807,7 +807,7 b' def _follow(repo, subset, x, name, follo'
             cx = c[x]
             s = set(ctx.rev() for ctx in cx.ancestors(followfirst=followfirst))
             # include the revision responsible for the most recent version
-            s.add(cx.linkrev())
+            s.add(cx.introrev())
         else:
             return baseset()
     else:

tests/test-log.t

@@ -1559,7 +1559,7 b' hg log -f dir across branches'
   o  a
   
   $ hg log -f d/a -T '{desc}' -G
-  o  b
+  @  c
   |
   o  a
   
@@ -1656,4 +1656,21 b' plain log lists the original version'
      date:        Thu Jan 01 00:00:00 1970 +0000
      summary:     content1
   
+
+hg log -f from the grafted changeset
+(The bootstrap should properly take the topology in account)
+
+  $ hg up 'desc(content3)^'
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg log -Gf a
+  @  changeset:   3:15b2327059e5
+  |  user:        test
+  |  date:        Thu Jan 01 00:00:00 1970 +0000
+  |  summary:     content2
+  |
+  o  changeset:   0:ae0a3c9f9e95
+     user:        test
+     date:        Thu Jan 01 00:00:00 1970 +0000
+     summary:     content1
+  
   $ cd ..