$wgHttpsPort should only be used in very special cases

$wgHttpsPort should only be used in very special cases

When expanding a URL, don't overwrite an explicitly specified port or
add a port to a foreign URL. $wgHttpsPort is only useful for a very
specific case: when $wgServer is protocol-relative and HTTPS is
requested.

Documented correct use of $wgHttpsPort in DefaultSettings.php. Fixed
invalid "@see", in Doxygen it can only point to "classes, functions,
methods, variables, files or URL".

Added test cases which previously failed.

Change-Id: Id65c58300d22712212b6605711ff916916e8768b