Allow builds to work with out of tree apr and apr-util

  Backported:
    buildconf: r1.30
    configure.in: r1.239, r1.240
, r1.242, r1.245
    server/mpm/config.m4 r1.47

  I suspect configure.in r1.244 should also be applied, I suspect so
  but want confirmation before backporting it.  If it's required, please
  simply commit that patch.

  Please *thoroughly* test so we uncover any vpath/out-of-tree/in-tree
  issues with apr/apr-util locations before our users do.  With everyone
  who voulenteered for the effort, this should be no hassle.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@98974 13f79535-47bb-0310-9956-ffa450edef68