add -p: warn if only binary changes present

Current 'git add -p' will say "No changes." if there are no changes to
text files, which can be confusing if there _are_ changes to binary
files.  Add some code to distinguish the two cases, and give a
different message in the latter one.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-add--interactive.perl

@@ -811,11 +811,16 @@ sub help_patch_cmd {
 }
 
 sub patch_update_cmd {
-	my @mods = grep { !($_->{BINARY}) } list_modified('file-only');
+	my @all_mods = list_modified('file-only');
+	my @mods = grep { !($_->{BINARY}) } @all_mods;
 	my @them;
 
 	if (!@mods) {
-		print STDERR "No changes.\n";
+		if (@all_mods) {
+			print STDERR "Only binary files changed.\n";
+		} else {
+			print STDERR "No changes.\n";
+		}
 		return 0;
 	}
 	if ($patch_mode) {