Rewrite mod_cgi's input handling to use brigades and input filters directly.

This removes the unnecessary overhead of the *_client_block functions.

Optimize usage of the dbuf char* (don't do pcalloc on it!)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@95376 13f79535-47bb-0310-9956-ffa450edef68