Quick update to r17088 - Fuzz testing was giving me a PHP Notice: "Undefined variable...

Quick update to r17088 - Fuzz testing was giving me a PHP Notice: "Undefined variable: wgUseDatabaseMessages in <b>/var/www/hosts/mediawiki/wiki/languages/messages/MessagesPl.php</b> on line <b>1292</b><br />". This happens because the desired output is the literal string "$wgUseDatabaseMessages", not the value of the $wgUseDatabaseMessages variable. However variables are not expanded in single quotes, but they are in double quotes; so when the line was changed from single to double quotes, it started wanting to print out the variable - therefore modifying to use single quotes, and adding escaping for the literal singles quotes.