filemerge: add support for change/delete conflicts to the ':local' merge tool

This covers two of the four cases of change/delete conflicts -- in an upcoming
patch we'll make :other cover the other two.

mercurial/filemerge.py

@@ -237,7 +237,7 b' def _iprompt(repo, mynode, orig, fcd, fc'
 @internaltool('local', nomerge)
 def _ilocal(repo, mynode, orig, fcd, fco, fca, toolconf):
     """Uses the local version of files as the merged version."""
-    return 0, False
+    return 0, fcd.isabsent()
 
 @internaltool('other', nomerge)
 def _iother(repo, mynode, orig, fcd, fco, fca, toolconf):