[PATCH next] test-lib: set $DIFF to diff if it is unset

[Thomas Rast <trast@student.ethz.ch>]

Since 7b3bdbb (fixup: do not unconditionally disable "diff -u",
2010-05-31), test-lib.sh depends on having $DIFF set in the
environment for the construction of $GIT_TEST_CMP.  While this works
when called from the main Makefile, it fails if the tests are called
on their own and the user does not have $DIFF set.

Set it to 'diff' if it is unset, like the Makefile does.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
---

I have an uneasy feeling that I must be missing something, seeing as
this went unnoticed for 10 days...

 t/test-lib.sh |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/t/test-lib.sh b/t/test-lib.sh
index b23a61d..4d89049 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -78,6 +78,7 @@ export EDITOR
 
 if test -z "$GIT_TEST_CMP"
 then
+	DIFF=${DIFF:-diff}
 	if test -n "$GIT_TEST_CMP_USE_COPIED_CONTEXT"
 	then
 		GIT_TEST_CMP="$DIFF -c"
-- 
1.7.1.550.g553ab5