Changed VisitorReturnFlag type from enum to const static size_t
updated alphabetaswap to support new visitors
updated alphaexpansion to support new visitors
updated alphaexpansionfusion to support new visitors
updated bruteforce to support new visitors
Merge pull request #188 from joergkappes/RC-2.3

refactoring Astar
* added begin() method to visitors to support inference algorithms which
don't provide a initial valid value or bound at 
* added missing initialization of member verbose_ in TimingVisitor
updated lpcplex to support new visitors
Merge remote-tracking branch 'opengm/RC-2.3' into RC-2.3
Merge pull request #189 from joergkappes/RC-2.3

arg return vec0s if no state is available
removed begin() method from new visitors
updated combilp to support new visitors
updated dynamicprogramming to support new visitors
Merge remote-tracking branch 'opengm/RC-2.3' into RC-2.3
updated graphcut to support new visitors
updated visitor to support gap limit
updated commandline tool to support new visitor (some algorithms are
deativated until they support the new visitor)
Merge pull request #190 from stopfer/RC-2.3

refactoring for new visitor
Merge pull request #49 from opengm/RC-2.3

update from opengm:RC-2.3