Skip man/html/completion generation if not needed

Skip man/html/completion generation if not needed

Make the man/html/completion targets use a stamp file to mark when they
were done, and do no rerun them if dependencies have not changed (most
notably, do not rerun them if nothing has changed, or if only test code
has changed).

Change-Id: I510e55cb4b4c798dfce2cc7d95d66d30e3e802c4