Hi Guix,

these patches add MIDI support to Frescobaldi via portmidi.  I took a
patch from Gentoo to break apart the portmidi build, so that we can
disable the Java parts and cleanly disable the tests which fail to link
(possibly because they are linked before “-lportmidi” is available).

Building the Java parts would make portmidi retain references to the JRE
(both in the pmjni library and in the pmdefaults tool) and I don’t think
this should be done for the basic version of this library to keep
closure size small.

I tested this with Frescobaldi, which now discovers the MIDI sequencer
device.

~~ Ricardo