Until now, we relied on setting MW_NO_SETUP which was a) hacky, b) irreversable, and c) likely to be forgotten if you didn't use one of the wrappers like runChild().
Instead, move the freaky magic to doMaintenance and have *it* check if it's in a specific call stack that indicates this is being run from the file scope and should be executed. Rename DO_MAINTENANCE to RUN_MAINTENANCE_IF_MAIN so it's nice and clear what magic happens behind the require_once().
