Cleanup of the `configure --shadow' process:

  - make sure the configure script creates its temporary files in the
    shadow tree to avoid conflicts with parallel configure runs
  - removed unnecessary option "-r" from "rm" call for Makefiles
  - make sure the configure scripts creates the shadow-wrapper Makefile
    only when no shadow trees already exists
  - make sure "make distclean" removes the shadow-wrapper Makefile but only
    when no more shadow trees exists
  - overhauled mkshadow.sh script: now its more IFS-safe and approx. twice
    as fast (in the past it needed 70sec, now it runs just 38sec)
  - make sure CVS does not complain about the created files
    Makefille.<gnutriple> and directories src.<gnutriple>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@81181 13f79535-47bb-0310-9956-ffa450edef68