[Verifier:New] Correct Prolog code for invokespecial

JSR 202 gave the following rule:

instructionIsTypeSafe(invokespecial(CP), Environment, _Offset, StackFrame, NextStackFrame, ExceptionStackFrame) :-
  ...
  thisClass(Environment, CurrentClass),
  reverse([CurrentClass | OperandArgList], StackArgList),
  ...
  currentClassLoader(Environment, L),
  reverse([class(MethodClassName, L) | OperandArgList], StackArgList2),
  ...
  isAssignable(class(CurrentClassName, L), class(MethodClassName, L)).

The last line is erroneous because CurrentClassName is undefined. We can't say class(CurrentClass, L) because CurrentClass is not a string but rather a class(...) term obtained from thisClass. But observe that currentClassLoader(Environment, L) is just a wrapper for thisClass, so we can just modify the call to thisClass and then simplify and correct the remainder:

instructionIsTypeSafe(invokespecial(CP), Environment, _Offset, StackFrame, NextStackFrame, ExceptionStackFrame) :-
  ...
  thisClass(Environment, class(CurrentClassName, L)),
  reverse([class(CurrentClassName, L) | OperandArgList], StackArgList),
  ...
  // No more currentClassLoader call. L is in scope thanks to thisClass.
  reverse([class(MethodClassName, L) | OperandArgList], StackArgList2),
  ...
  isAssignable(class(CurrentClassName, L), class(MethodClassName, L)).