Merge pull request #64 from DerThorsten/RC2.1

Rc2.1
Merge pull request #5 from opengm/RC2.1

Rc2.1
remove fills in dualdecomp, change OPTIMAL to PASS in Gibbs test, add OPENGM_DEBUG flag for tests
Merge pull request #66 from joergkappes/RC2.1

bugfixes