test-lib-functions.sh: add lf_to_nul helper

Add lf_to_nul helper function to test-lib-functions.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib-functions.sh

@@ -81,6 +81,10 @@ test_decode_color () {
 	'
 }
 
+lf_to_nul () {
+	perl -pe 'y/\012/\000/'
+}
+
 nul_to_q () {
 	perl -pe 'y/\000/Q/'
 }