Issue 3605: bagpipe corrections and additions

Issue 3605: bagpipe corrections and additions

Contributed by Julia Meihoefer and Oliver Briede:

   Our corrections are based on research we did for Julia's Bachelor
   Thesis in computer engineering 'Identification, notation and
   reproduction of the Great Highland Bagpipe sound' in August 2014.

This change does NOT include any conversion rules for the the
following noteworthy changes:

  * remove \gcatcha, \gcatchb ... \gcatche
  * rename \dgrip to \bgrip
  * rename \dtaor to \btaor