Get rid of the accept abstraction, which seems out-of-place in the MPM

codebase, and make the poll-accept model the only model supported. Also,
some code was cleaned up and rewritten in the process.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@83446 13f79535-47bb-0310-9956-ffa450edef68