throw error if method ref to resolve not declared in class

VM.execute currently throws the vague error:

```
TypeError: methodInfo is undefined vm.js:996
```

Or, in Chrome:

```
Uncaught TypeError: Cannot read property 'signature' of undefined vm.js:996
```

This turns out to be because the FrameAnimator.java stub doesn't declare the `register` method, which a MIDlet I'm testing is calling. Here's a change that throws this better error message, so a problem like this is easier to debug:

```
Error: com/nokia/mid/ui/frameanimator/FrameAnimator.register.(IISSLcom/nokia/mid/ui/frameanimator/FrameAnimatorListener;)Z not declared in class vm.js:138
```

Presumably this failure should actually raise some Java exception, though.