largefiles: fall back to the original for change/delete conflicts

The largefiles merge code (currently) does not handle change/delete conflicts.
So fall back to regular filemerge in that case.

Making this code handle change/delete conflicts is left as an exercise for the
future.

hgext/largefiles/overrides.py

@@ -544,7 +544,7 b' def mergerecordupdates(orig, repo, actio'
 # largefiles. This will handle identical edits without prompting the user.
 def overridefilemerge(origfn, premerge, repo, mynode, orig, fcd, fco, fca,
                       labels=None):
-    if not lfutil.isstandin(orig):
+    if not lfutil.isstandin(orig) or fcd.isabsent() or fco.isabsent():
         return origfn(premerge, repo, mynode, orig, fcd, fco, fca,
                       labels=labels)