dagop: use fctx.rev() consistently in filectxancestors()

We can't use fctx.linkrev() to sort fctxs coming from multiple files.
This was changed at a5b8b1052ef6 due to performance issue, but we know
we evaluate parent.rev() in revset anyway.

mercurial/dagop.py

@@ -87,7 +87,7 @@ def filectxancestors(fctx, followfirst=False):
     yield c
     while True:
         for parent in c.parents()[:cut]:
-            visit[(parent.linkrev(), parent.filenode())] = parent
+            visit[(parent.rev(), parent.filenode())] = parent
         if not visit:
             break
         c = visit.pop(max(visit))