mergetool: don't skip modify/remove conflicts

mergetool: don't skip modify/remove conflicts

Since bb0a484 (mergetool: Skip autoresolved paths, 2010-08-17),
mergetool uses different ways of figuring out the list of files with
merge conflicts depending on whether rerere is active. If rerere is
active, mergetool will use 'git rerere status' to list the files with
remaining conflicts. However, the output from that command does not
list conflicts of types that rerere does not handle, such as
modify/remove conflicts.

Another problem with solely relying on the output from 'git rerere
status' is that, for new conflicts that are not yet known to rerere,
the output from the command will list the files even after adding them
to the index. This means that if the conflicts in some files have been
resolved and 'git mergetool' is run again, it will ask the user
something like the following for each of those files.

 file1: file does not need merging
 Continue merging other unresolved paths (y/n) ?

Solve both of these problems by replacing the call to 'git rerere
status' with a call to the new 'git rerere remaining' that was
introduced in the previous commit.

Signed-off-by: Martin von Zweigbergk <martin.von.zweigbergk@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>