MethodExpression typecheck fails to select implementations wher argument type is subtype of formal parameter

When a MethodExpression is being type checked the type checker considers all overloaded version of the method as implementation candidates for the call. It prunes any candidates by iteratively comparing successive argument types with the corresponding formal types. However, it should actually ensure that the argument type is assignable to the formal type rather than equal to it.

As an example, consider the following built-in call

traceStack("foo", "bar").

Helper implements two possible candidates

traceStack(String prefix, Object key)

and

traceStack(String prefix, int maxFrames)

Clearly the first one should be selected and the second one rejected. In fact, neither is accepted.