t1400: make test debuggable.

I had a hard time figuring out why this test was failing with
the packed-refs update without running it under "sh -x".  This
makes output from "sh t1400-update-ref.sh -v" more descriptive.

Updating other tests would be a good janitorial task.

Signed-off-by: Junio C Hamano <junkio@cox.net>