test: consolidate definition of $LF

As we seem to need this variable that holds a single LF character
in many places, define it in test-lib.sh and let the test scripts
use it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib.sh

@@ -92,6 +92,10 @@ _x40="$_x05$_x05$_x05$_x05$_x05$_x05$_x05$_x05"
 # Zero SHA-1
 _z40=0000000000000000000000000000000000000000
 
+# Line feed
+LF='
+'
+
 # Each test should start with something like this, after copyright notices:
 #
 # test_description='Description of this test...