Rearchitect the mess in http_main.c, http_core.c and buff.c.

Rearchitect the mess in http_main.c, http_core.c and buff.c.
Basic restructuring to introduce the MPM concept; includes various
changes to the module API... better described by docs/initial_blurb.txt.

Created multiple process model (MPM) concept by ripping out the process
guts from http_main.c and http_core.c and moving them to separate files
under src/modules/mpm/

Moved socket creation stuff to listen.c.
Moved connection open, maintenance and close to http_connection.c.

I/O layering and BUFF revamp.  Much of buff.c moved to ap_iol,
iol_socket, and iol_file.  See docs/buff.txt.

Moved user and auth fields from connection_rec to request_rec.
Removed RLIMIT stuff, supposedly to be implemented later in mod_cgi.
Disabled suexec, supposedly to be reimplemented later.

Submitted by:	Dean Gaudet

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@83763 13f79535-47bb-0310-9956-ffa450edef68