Catch Error exceptions in MediaWiki::run()

Catch Error exceptions in MediaWiki::run()

This avoids triggering other exceptions down the road such as
"Got COMMIT while atomic sections FileDeleteForm::doDelete,
LocalFile::lockingTransaction are still open". Those would
happen in LBFactory::__destruct(), when it tries to commit any
dangling transactions (firing attached callbacks too). Just like
with the Exception case, the DBs needs to all be rolled back.

Also make LoadBalancer::rolbackMasterChanges() rollback any
explicit transactions even if they have no pending changes.
This clears up the state to avoid later atomic section errors.

Change-Id: Ic0b6b12c1edc1eec239f4f048359b3bbb497d3ff