MPM event:

- Keep track of the number of clogged, lingering, and suspended connections.
- Don't count connections in lingering close state when calculating
  how many additional connections may be accepted

Backport of r1361773 and r 1361778 from trunk.

Submitted by: sf
Reviewed by: rjung, jim
Backported by: rjung


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1369473 13f79535-47bb-0310-9956-ffa450edef68