merge r956059, 1000130, and 1000474 from trunk:

improve connection pooling overview and descriptions of
min, max, smax, and ttl parameters


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@1050958 13f79535-47bb-0310-9956-ffa450edef68