Patch 993768 on the SF page tracker.
It's a midi input driver for Windows. Allegro has a midi input interface. I
don't think it's used that often, but it's there and (according to the
docs) only available for DOS.
If there are no problems with this patch (I'm particularly concerned with
adding global symbols to the library here), then I think it could be
included. Someone who knows something about Allegro's midi subsystem, in
particular the Windows implementation of it, should take a look at it
though.