[PATCH 4 of 6 mergedriver] filemerge: in ':prompt', use ':fail' tool rather than returning directly

[Siddharth Agarwal]

# HG changeset patch
# User Siddharth Agarwal <sid0 at fb.com>
# Date 1448391515 28800
#      Tue Nov 24 10:58:35 2015 -0800
# Node ID b2436682a9f6f8b56b768475004aecf57cab6677
# Parent  2ba8e74e9de139060fdbe67ac769e5fcf0f27651
# Available At http://42.netv6.net/sid0-wip/hg/
#              hg pull http://42.netv6.net/sid0-wip/hg/ -r b2436682a9f6
filemerge: in ':prompt', use ':fail' tool rather than returning directly

The ':fail' tool now knows to write out the changed side for change/delete
conflicts.

This has no impact right now but will make things better when we move
change/delete conflicts in here.

diff --git a/mercurial/filemerge.py b/mercurial/filemerge.py
--- a/mercurial/filemerge.py
+++ b/mercurial/filemerge.py
@@ -260,7 +260,7 @@ def _iprompt(repo, mynode, orig, fcd, fc
             return _ilocal(repo, mynode, orig, fcd, fco, fca, toolconf)
     except error.ResponseExpected:
         ui.write("\n")
-        return 1, False
+        return _ifail(repo, mynode, orig, fcd, fco, fca, toolconf)
 
 @internaltool('local', nomerge)
 def _ilocal(repo, mynode, orig, fcd, fco, fca, toolconf):