* Add support for forward references of global variable addresses

* Add support for numeric global variable addresses
* Clean up getVal function by refactoring it into several smaller functions
* MethodTypes are now specified with an explicit isVarArg parameter
* Break ValueRef into ConstValueRef & SymbolicValueRef components
* Add support for the new Invoke instruction
* Fix a few broken calls to Type::getName instead of Type::getDescription

llvm-svn: 758