git add -p: new "quit" command at the prompt.

There's already 'd' to stop staging hunks in a file, but no explicit
command to stop the interactive staging (for the current files and the
remaining ones).  Of course you can do 'd' and then ^C, but it would be
more intuitive to allow 'quit' action.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-add.txt

@@ -245,6 +245,7 @@ patch::
 
        y - stage this hunk
        n - do not stage this hunk
+       q - quite, do not stage this hunk nor any of the remaining ones
        a - stage this and all the remaining hunks in the file
        d - do not stage this hunk nor any of the remaining hunks in the file
        j - leave this hunk undecided, see next undecided hunk

git-add--interactive.perl

@@ -890,6 +890,7 @@ sub help_patch_cmd {
 	print colored $help_color, <<\EOF ;
 y - stage this hunk
 n - do not stage this hunk
+q - quit, do not stage this hunk nor any of the remaining ones
 a - stage this and all the remaining hunks in the file
 d - do not stage this hunk nor any of the remaining hunks in the file
 g - select a hunk to go to
@@ -926,7 +927,7 @@ sub patch_update_cmd {
 					@mods);
 	}
 	for (@them) {
-		patch_update_file($_->{VALUE});
+		return 0 if patch_update_file($_->{VALUE});
 	}
 }
 
@@ -972,6 +973,7 @@ sub display_hunks {
 }
 
 sub patch_update_file {
+	my $quit = 0;
 	my ($ix, $num);
 	my $path = shift;
 	my ($head, @hunk) = parse_diff($path);
@@ -1002,6 +1004,11 @@ sub patch_update_file {
 				$_->{USE} = 0 foreach ($mode, @hunk);
 				last;
 			}
+			elsif ($line =~ /^q/i) {
+				$_->{USE} = 0 foreach ($mode, @hunk);
+				$quit = 1;
+				last;
+			}
 			else {
 				help_patch_cmd('');
 				next;
@@ -1109,6 +1116,16 @@ sub patch_update_file {
 				}
 				next;
 			}
+			elsif ($line =~ /^q/i) {
+				while ($ix < $num) {
+					if (!defined $hunk[$ix]{USE}) {
+						$hunk[$ix]{USE} = 0;
+					}
+					$ix++;
+				}
+				$quit = 1;
+				next;
+			}
 			elsif ($line =~ m|^/(.*)|) {
 				my $regex = $1;
 				if ($1 eq "") {
@@ -1235,6 +1252,7 @@ sub patch_update_file {
 	}
 
 	print "\n";
+	return $quit;
 }
 
 sub diff_cmd {