Add some comments and error checking code to avoid wild memcpy.

This doesn't fix any of the code, just makes it hurt less.  Major
bogosity here.

PR:
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git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@81724 13f79535-47bb-0310-9956-ffa450edef68