gosam-contrib-higherrank: golem95 higher-rank pentagon fix

This commit fixes the rank-6 pentagons and the corresponding tens_rec functions.
Additionally, some lower rank pentagons are simplified.

git-svn-id: svn+ssh://svn.hepforge.org/hepforge/svn/gosam/gosam-contrib-higherrank@428 a6e02f90-e1d0-4296-904b-e314d7e4afaa