Bug 126

I used gigedit to change the pitch bend range in the instruments at
maestro_concert_grand_v2.gig and hit the "save" button. It took about three
hours. Besides the GUI froze.

While it should be possible to design a more intelligent save method that tried
to optimize disk writes, it would probably be much, much easier and almost
equally effective at a first moment to implement multifile gig write support for
working with really big gigs.

A nice extra when time and motivation permits would be some progress callback
from the save methods, but let's get the editor(s) rolling first.