test-commit-amend: exhibit an --amend weirdness

The weirdness is --amend let you replace one file with another with same data
and flags if the new file copy record differ from the one in the parent
revision. In theory, there is no problem with this kind of thing, subversion
supports it, but here we see log and status disagree. The reason is log reads
the copy record from the filelog, while status calls copies.pathcopies() which
eventually invokes some expensiveness argument to discard this case (copies.py,
_forwardcopies(), line 132). Since the next patch will side with pathcopies(),
I prefer to call this behaviour a bug.

tests/test-commit-amend.t

@@ -287,6 +287,18 b' Follow copies/renames:'
   A f
     d
 
+  $ mv f f.orig
+  $ hg rm -A f
+  $ hg ci -m removef
+  $ hg cp a f
+  $ mv f.orig f
+  $ hg ci --amend -m replacef
+  saved backup bundle to $TESTTMP/.hg/strip-backup/0ce2c92dc50d-amend-backup.hg
+  $ hg st --change . --copies
+  M f
+  $ hg log -r . --template "{file_copies}\n"
+  f (a)
+
 Can't rollback an amend:
 
   $ hg rollback