The refresh pass does not correctly keep track of the scope of local variables
and can convert things like \x->(\x->x) x into \x1->(\x2->x2) x2. Fortunately,
it appears that the refresh pass is not needed anymore, so it has been removed.
This speeds up the compilation of PhrasebookFin.pgf by 12%, mosly by speeding
up calls to lookupModule in calls from lookupParamValues, in calls
from allParamValues.
The invariant "modules are stored in dependency order" is no longer respected!
But the type MGrammar is now abstract, making it easier to maintain this or
other invariants in the future.
