(bug 14990) Don't hardcode MySQL backticks in table names for parser tests. Instead...

(bug 14990) Don't hardcode MySQL backticks in table names for parser tests.  Instead, switch the database prefix back and forth.  This doesn't seem to either trash my wiki or change how well the parser tests run, but if you run this on Wikipedia without testing please don't blame me if it drops all tables on the   :)

  Of course, $wgDBprefix is not meant to be changed a few dozen times every time a script is run, but I don't think it will cause problems.  If it does, an alternative would be supporting a $prefix parameter to Database::tableName().