Use 'trash directory' thoroughly in t/test-lib.sh

...also in comments.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib.sh

@@ -386,7 +386,7 @@ test_done () {
 }
 
 # Test the binaries we have just built.  The tests are kept in
-# t/ subdirectory and are run in trash subdirectory.
+# t/ subdirectory and are run in 'trash directory' subdirectory.
 PATH=$(pwd)/..:$PATH
 GIT_EXEC_PATH=$(pwd)/..
 GIT_TEMPLATE_DIR=$(pwd)/../templates/blt