Revision 3710

* gig.cpp: Added methods Region::UsesAnyGigFormatExtension(),
  Instrument::UsesAnyGigFormatExtension() and
  File::UsesAnyGigFormatExtension() (as private methods for
  now, see comments on methods for reason why).

* gig.cpp: Only write pure-GSt-compatibility RIFF chunks
  introduced by SVN r3657 if the file is not using any of
  our gig format extensions anyway.

* Bumped version (4.2.0.svn6).