[PATCH] Add --diff-filter= output restriction to diff-* family.

This is a halfway between debugging aid and a helper to write an
ultra-smart merge scripts.  The new option takes a string that
consists of a list of "status" letters, and limits the diff
output to only those classes of changes, with two exceptions:

 - A broken pair (aka "complete rewrite"), does not match D
   (deleted) or N (created).  Use B to look for them.

 - The letter "A" in the diff-filter string does not match
   anything itself, but causes the entire diff that contains
   selected patches to be output (this behaviour is similar to
   that of --pickaxe-all for the -S option).

For example,

    $ git-rev-list HEAD |
      git-diff-tree --stdin -s -v -B -C --diff-filter=BCR

shows a list of commits that have complete rewrite, copy, or
rename.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff-helper.c

@@ -8,17 +8,16 @@
 static const char *pickaxe = NULL;
 static int pickaxe_opts = 0;
 static const char *orderfile = NULL;
+static const char *diff_filter = NULL;
 static int line_termination = '\n';
 static int inter_name_termination = '\t';
 
 static void flush_them(int ac, const char **av)
 {
-	diffcore_std(av + 1,
-		     0, 0, /* no renames */
-		     pickaxe, pickaxe_opts,
-		     -1, /* no breaks */
-		     orderfile);
-	diff_flush(DIFF_FORMAT_PATCH, 0);
+	diffcore_std_no_resolve(av + 1,
+				pickaxe, pickaxe_opts,
+				orderfile, diff_filter);
+	diff_flush(DIFF_FORMAT_PATCH);
 }
 
 static const char *diff_helper_usage =
@@ -38,6 +37,10 @@ int main(int ac, const char **av) {
 		}
 		else if (!strcmp(av[1], "--pickaxe-all"))
 			pickaxe_opts = DIFF_PICKAXE_ALL;
+		else if (!strncmp(av[1], "--diff-filter=", 14))
+			diff_filter = av[1] + 14;
+		else if (!strncmp(av[1], "-O", 2))
+			orderfile = av[1] + 2;
 		else
 			usage(diff_helper_usage);
 		ac--; av++;