Add 'filter' attribute and external filter driver definition.

The interface is similar to the custom low-level merge drivers.

First you configure your filter driver by defining 'filter.<name>.*'
variables in the configuration.

	filter.<name>.clean	filter command to run upon checkin
	filter.<name>.smudge	filter command to run upon checkout

Then you assign filter attribute to each path, whose name
matches the custom filter driver's name.

Example:

	(in .gitattributes)
	*.c	filter=indent

	(in config)
	[filter "indent"]
		clean = indent
		smudge = cat

Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 9 insertions, 0 deletions

diff --git a/t/t0021-conversion.sh b/t/t0021-conversion.sh
index ad952c9..bab9ecc 100755
--- a/t/t0021-conversion.sh
+++ b/t/t0021-conversion.sh
@@ -4,8 +4,17 @@ test_description='blob conversion via gitattributes'
 
 . ./test-lib.sh
 
+cat <<\EOF >rot13.sh
+tr '[a-zA-Z]' '[n-za-mN-ZA-M]'
+EOF
+chmod +x rot13.sh
+
 test_expect_success setup '
+	git config filter.rot13.smudge ./rot13.sh &&
+	git config filter.rot13.clean ./rot13.sh &&
+
 	{
+	    echo "*.t filter=rot13"
 	    echo "*.i ident"
 	} >.gitattributes &&