fixed hashCode for SymbolicConstraint; refactored hashCode caching
fixed bug introduced in previous commit by caching the hash code for SymbolicConstraint and SymbolicConstraint.Equality
added copyright
first draft of visitor refactoring

this commit breaks everything ever, I know. But I want to get reviews done on the interface for visitors before I start making changes to the entire code base to support the new API.

Note that while I'm sure I'll have to do some fine-tuning, this is designed to serve as a drop-in replacement for what already existed, except that BasicHookWorker has now become
LocalTransformer in keeping with its similarity in function to LocalTransformer in org.kframework.backend.java
add generic throws parameter, plus remove type parameters from drop-in replacement visitors
remove more type parameters to make this easier to replace legacy code
made SymbolicConstraint#Equality immutable
Adding test for symbolic backend.
Fixing NullPointerException in symbolic backend.
Fixing the symbolic backend: require --backend symbolic for krun; fixed the smt solver (missing) call.
Added a regression test for the symbolic backend, which tests all its important features.
first draft of code to make everything compile
Changed checkstyle to check for a lowercase copyright symbol to be consistent
with the LICENSE file.
Updated copyrights for the new copyright check.
fix the remaining compiler errors, plus do some cleanup and fix bugs
Merge branch 'master' into visitor

Conflicts:
	src/javasources/KTool/src/org/kframework/backend/symbolic/AddPCToBagVariable.java
	src/javasources/KTool/src/org/kframework/backend/symbolic/ResolveLtlAttributes.java
	src/javasources/KTool/src/org/kframework/kil/KList.java
	src/javasources/KTool/src/org/kframework/kil/UserList.java
	src/javasources/KTool/src/org/kframework/kil/visitors/BasicTransformer.java
add copyright
fix some inconsistencies in AbstractVisitor
Added copyright forms.
more fixes to SymbolicConstraint#Equality