Merge pull request #57 from opengm/RC-2.3

update from opengm:master
Merge pull request #58 from opengm/RC-2.3

update from opengm:master
Merge pull request #59 from opengm/RC-2.3

update from opengm:master
Merge pull request #60 from opengm/RC-2.3

update from opengm:master
Use new CMAKE-CPLEX-VARS
Merge pull request #224 from joergkappes/RC-2.3

Update CMAKE-CPLEX-VARS for Python