pg_ctl patch to integrate apache's rotatelogs

Please find attached a patch to integrate rotatelogs into pg_ctl. I've
noticed a couple of questions about how to do this and it seems easier
(and more elegant) to solve it in code rather than in documentation. The
patch is pretty simple and I've made it reasonably self documenting. It
test for apache rotatelogs only when unless it is specifically used.
This code only adds functionality and causes no changes to current usage.

If anyone has suggestions how I could improve it or make it more
acceptable in any way, I'd very much like to hear them.

Andrew Hammond