core: Add the option to keep aside a request body up to a certain

size that would otherwise be discarded, to be consumed by filters
such as mod_include. When enabled for a directory, POST requests
to shtml files can be passed through to embedded scripts as POST
requests, rather being downgraded to GET requests.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@592951 13f79535-47bb-0310-9956-ffa450edef68