split Cell2DS and JavaBackendCell2DS properly; fixed JavaBackendCell2DS
fixed RewriteEngineUtils#evaluateConditions
fixed side condition evaluation properly
added some comment
added defensive code for concatenating two maps with common keys
relaxed the check of AC-Matching to be more accurate
fixed ConstrainedTerm#unify; added defensive code to check unsplit disjuctions
excluded rules with AC-matching in side-conditions from fast rewriting; added TODO comment
added regression test
Merge pull request #1114 from yilongli/fix-java-backend

Fix java backend