Adds support for reading trailers on input by exporting get_mime_headers

to ap_get_mime_headers and calling it in the appropriate place in
ap_http_filter.

showstoppers--;


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@94667 13f79535-47bb-0310-9956-ffa450edef68