Forward port 1.3 overhaul of isapi to 2.0.

  Yes - it's blatently obvious that this should be 'bucketized', but the
  sequence I will follow is:

    *) compatibility of sources
    *) extension to async + transmitfile emulated support
    *) localization of ISAPI* directives to Directory, File blocks
    *) addition of ISAPI caching
    *) recode for buckets.

  I'm actually looking forward to the mod_cgi bucketization as a model.

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git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86360 13f79535-47bb-0310-9956-ffa450edef68