rule-based and heuristic build are now relying on the same implementation for backbone torsion angles
-removed isp torsion completely
-fixed omega torsion implementation 
+added check for res.IsPetideLinking() before adding backbone torsions


git-svn-id: https://dng.biozentrum.unibas.ch/svn/openstructure/trunk@1896 5a81b35b-ba03-0410-adc8-b2c5c5119f08