Draft: MR for code review of branch 'impact-stop-join'

This branch implements new stop operators stop-join for ARGCPA, CompositeCPA and PredicateCPA. stop-join could work with Impact and Predicate refinement. The experimental evaluation (Impact, Predicate) shows that stop-join could solve several cases where stop-sep timeout.

This merge request is for code review and discussions only. Merge must be done with svn merge.