Improve phpdoc of 'OldRestrictions' in Title

Improve phpdoc of 'OldRestrictions' in Title

The previous version of the phpdoc simply says
that the field contains a comma seperated list of
page restrictions, which is wrong.
The field is actually a colon seperated list of comma
seperated lists.

The new phpdoc and example have been pulled from mw.org
and checked against what actually exists in a real db.

Change-Id: I6bfdfd87120150e4b53e1b4c49e95041f55d8c97