Follow-up to r1592529:

Define default port for "scgi" schemes (as chosen by
mod_proxy_scgi) in a common location.

Suggested by: jailletc36


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1592615 13f79535-47bb-0310-9956-ffa450edef68