no need to rename rule vars since we always use pattern-matching for function evaluation
fixed some latent bugs introduced by the new AC collection; improved CellCollection#toString
Merge branch 'unified-builtins2' into preserve-rule-var-original-name

Conflicts:
	src/javasources/KTool/src/org/kframework/backend/java/symbolic/KILtoBackendJavaKILTransformer.java
Merge pull request #777 from yilongli/preserve-rule-var-original-name

improve intermediate debugging messages printed by the prover