tests: provide $TRASH_DIRECTORY variable

Most scripts don't care about the absolute path to the trash
directory. The one exception was t4014 script, which pieced
together $TEST_DIRECTORY and $test itself to get an absolute
directory.

Instead, let's provide a $TRASH_DIRECTORY which specifies
the same thing. This keeps the $test variable internal to
test-lib.sh and paves the way for trash directories in other
locations.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4014-format-patch.sh

@@ -493,13 +493,12 @@ test_expect_success 'format-patch from a subdirectory (2)' '
 '
 
 test_expect_success 'format-patch from a subdirectory (3)' '
-	here="$TEST_DIRECTORY/$test" &&
 	rm -f 0* &&
 	filename=$(
 		rm -rf sub &&
 		mkdir -p sub/dir &&
 		cd sub/dir &&
-		git format-patch -1 -o "$here"
+		git format-patch -1 -o "$TRASH_DIRECTORY"
 	) &&
 	basename=$(expr "$filename" : ".*/\(.*\)") &&
 	test -f "$basename"

t/test-lib.sh

@@ -645,7 +645,8 @@ fi
 
 # Test repository
 test="trash directory.$(basename "$0" .sh)"
-test ! -z "$debug" || remove_trash="$TEST_DIRECTORY/$test"
+TRASH_DIRECTORY="$TEST_DIRECTORY/$test"
+test ! -z "$debug" || remove_trash=$TRASH_DIRECTORY
 rm -fr "$test" || {
 	GIT_EXIT_OK=t
 	echo >&5 "FATAL: Cannot prepare test area"