rotatelogs: Add support for running a custom program after a log

rotation.

* support/rotatelogs.c (post_rotate): New function.
  (usage, dumpConfig): Update.
  (doRotate): Save old filename before rotate; call post_rotate after
  successful rotation.
  (main): Add -p argument.

* docs/manual/programs/rotatelogs.xml: Document -p.

PR: 51285
Submitted by: <sveniu ifi.uio.no>, jorton


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1137590 13f79535-47bb-0310-9956-ffa450edef68