test overlapping ignore patterns

Add a test which checks that negated patterns such as "!foo.html" can
override previous patterns such as "*.html". This is documented
behaviour but had not been tested so far.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3001-ls-files-others-exclude.sh

@@ -140,4 +140,10 @@ test_expect_success 'trailing slash in exclude forces directory match (2)' '
 
 '
 
+test_expect_success 'negated exclude matches can override previous ones' '
+
+	git ls-files --others --exclude="a.*" --exclude="!a.1" >output &&
+	grep "^a.1" output
+'
+
 test_done