- Fixed issue  8: missing default value on cone_enable soho parameter
- Fixed issue  9: fixed check for absolute and relative path
- Fixed issue 10: missing shader paths give a warning now

Further bug fixes/enhancements:
- Cleaned up the appleseed ROP, some parameters for debuggin and testing removed
- Updated INSTALL.txt
- Fixed issue with instances not being properly written to in the case where
  an object had several materials.