- added the set_error_tolerance_factor function to ModBaseT and implemented it in inherited classes as necessary
- added the set_error_tolerance_factor function to BaseDecimaterT, which calls set_error_tolerance_factor for all loaded Mods
- implemented a decimate_constraints_only function for the McDecimater (and adjusted the MixedDecimater accordingly)
- implemented stop criterions for the McDecimater
- added some OpenMP loops for the sample generation to the McDecimater

git-svn-id: http://www.openmesh.org/svnrepo/OpenMesh/trunk@685 fdac6126-5c0c-442c-9429-916003d36597