mod_proxy: follow up to r1750301.

s/is_socket_connected/get_socket_connected/ in the !USE_ALTERNATE_IS_CONNECTED
case, and add CHANGE + MMN entries.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1750305 13f79535-47bb-0310-9956-ffa450edef68