Provide apr_pool_t arg to register_hooks, since anything they do in that
  step -must- be done with a pool that will not outlive the cmd pool, from
  which they may have been dynamically loaded.

  This needs further review, it's committed only as a stopgap for those
  who's builds I broke, sorry.  Review tbc late this evening.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@87699 13f79535-47bb-0310-9956-ffa450edef68