Mozart kv315 update to 2.18.0

In addition to updating:
* fixed an error in Oboe I at measure 23
* two files (horns.ly, oboi.ly) contained cut & paste variables from other files (horn1.ly, horn2.ly, oboe1.ly, and oboe2.ly); usage was converted to partcombines of the appropriate elements.
* Makefile was modified to build pdf's

Closes issue #255