Accelerate mod_dumpio processing;

 * drop a frequent query for the mod configuration (pass as f->ctx)
 * drop one copy, at least for ASCII

and ensure larger buffers are logged in their entirety.  Some clarity
in output can be added by designating continuations vs first lines.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@750126 13f79535-47bb-0310-9956-ffa450edef68