A few command line options accepted by pg_regress were not being output
by help(), including --help itself. Add that one, as well as --version
and --bindir, and the corresponding short options for the first two.

We could consider this for backpatching, but it did not seem worthwhile
and no one else advocated for it, so apply only to master for now.

Author: Joe Conway
Reviewed-By: Tom Lane
Discussion: https://postgr.es/m/dd519469-06d7-2662-83ef-c926f6c4f0f1%40joeconway.com