Fix 204 handling. This moves some logic that used to be in

ap_send_error_response to the http_header filter.  The reason for the move,
is that the header filter takes care of all header processing now.  Without
this change, we were sending garbage data to the client whenever we sent
304 responses.
Submitted by:	Brian Havard and Ryan Bloom


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@87003 13f79535-47bb-0310-9956-ffa450edef68