enhanced builin equality for symbolic terms
made SymbolicConstraint#Equality immutable

Conflicts:
	src/javasources/KTool/src/org/kframework/backend/java/symbolic/SymbolicConstraint.java
minor
Merge pull request #517 from andreistefanescu/unified-builtins2

enhanced builtin equality for symbolic terms; fix for immutable SymbolicConstraint#Equality