intvecs: Converted hand controllers, keyboard and synth to be slot devices,
by using a temporary hack to workaround the impossibility to plug the same
device into 2 different slots as these keyboard require. [Fabio Priuli]
out of whatsnew: in the long term we need to come up with a core solution
for these devices that occupy multiple slot devices at once (another one is
the VCS Compumate which plugs into both VCS control ports), because the
hack I used (a "fake" control port which acts as a passthru for the two real
control ports) is not really satisfactory. However, current solution is better
than the selectable controllers we had, which were (ab)using
PORT_CONDITIONs...
