*8854* Added tests for getRemoteAddr trust_x_forwarded_for config setting

Added unit tests for http://pkp.sfu.ca/bugzilla/show_bug.cgi?id=8854
FWIW, if you use this pattern:
https://github.com/pkp/pkp-lib/blob/ojs-stable-2_4/classes/config/Config.inc.php#L94
...the get happens by reference, so the later set isn't required.