CommonMessaging: allow msgLevel to be called early

ATLAS uses a series of messaging macros to check the level of the MsgStream before doing output, saving a lot of time spent in ostream manipulation. This requires the MsgStream object to be created when msgLevel() is called, which is not guaranteed if the macro is used before the component is initialized (where setUpMessaging() is normally called). This is also a problem with genconf, which does not call initialize.