MODQT_* values.
This makes it possible to include both qt3 and qt4, as long as one is
very careful in choosing the right variables, without any change for the
existing qt3-only, qt4-only ports.
We don't bother with qt and qt2 as they are mostly end-of-life.
- stop supporting !mt, since it has worked for a long time.
- mt becomes a pseudo_flavor for compat purposes.
- merge base back into the main module.
- link mt names to not mt names.
- finish recreating a full QTDIR structure for compatibility as well.
