linkrev: also adjust linkrev when bootstrapping annotate (issue4305)

The annotate logic now use the new 'introrev' method to bootstrap its traversal.
This catches issues from linkrev-shadowing of the changeset introducing the
version of a file in source changeset.

More tests have been added to display pathological cases.

mercurial/context.py

@@ -877,10 +877,11 b' class basefilectx(object):'
             return pl
 
         # use linkrev to find the first changeset where self appeared
-        if self.rev() != self.linkrev():
-            base = self.filectx(self.filenode())
-        else:
-            base = self
+        base = self
+        introrev = self.introrev()
+        if self.rev() != introrev:
+            base = filectx(self._repo, self._path, filelog=self.filelog(),
+                           fileid=self.filenode(), changeid=introrev)
 
         # This algorithm would prefer to be recursive, but Python is a
         # bit recursion-hostile. Instead we do an iterative

tests/test-annotate.t

@@ -510,4 +510,10 b' Annotate should list ancestor of startin'
   3: B
   4: C
 
+Even when the starting revision is the linkrev-shadowed one:
+
+  $ hg annotate a -r 3
+  0: A
+  3: B
+
   $ cd ..