grep: add --heading

With --heading, the filename is printed once before matches from that
file instead of at the start of each line, giving more screen space to
the actual search results.

This option is taken from ack (http://betterthangrep.com/).  And now
git grep can dress up like it:

	$ git config alias.ack "grep --break --heading --line-number"

	$ git ack -e --heading
	Documentation/git-grep.txt
	154:--heading::

	t/t7810-grep.sh
	785:test_expect_success 'grep --heading' '
	786:    git grep --heading -e char -e lo_w hello.c hello_world >actual &&
	808:    git grep --break --heading -n --color \

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/Documentation/git-grep.txt b/Documentation/git-grep.txt
index dea7cad..07b3c6a 100644
--- a/Documentation/git-grep.txt
+++ b/Documentation/git-grep.txt
@@ -151,6 +151,10 @@ OPTIONS
 --break::
 	Print an empty line between matches from different files.
 
+--heading::
+	Show the filename above the matches in that file instead of
+	at the start of each shown line.
+
 -[ABC] <context>::
 	Show `context` trailing (`A` -- after), or leading (`B`
 	-- before), or both (`C` -- context) lines, and place a