AP_ENABLE_V4_MAPPED with WinNT MPM

  mpm_winnt.c: Fail to compile if enabled, and add a hint about the
               issue to address before it will work.
  configure.in: Move the --enable-v4-mapped check to below the
                MPM logic, and default to --disable-v4-mapped if
                using the WinNT MPM


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1091467 13f79535-47bb-0310-9956-ffa450edef68