tests: add missing trailing 'cd ..' Many tests didn't change back from subdirectories at the end of the tests ... and they don't have to. The missing 'cd ..' could always be added when another test case is added to the test file. This change do that tests (99.5%) consistently end up in $TESTDIR where they started, thus making it simpler to extend them or move them around.

--- a/tests/test-diffstat.t
+++ b/tests/test-diffstat.t
@@ -69,3 +69,4 @@
    file with spaces |  Bin 
    1 files changed, 0 insertions(+), 0 deletions(-)
 	
+  $ cd ..