Fixes 417. Error now shows on nonexstent function.

You now get the error
"Undefined Variable Name 'blarg'."
If you try to run a non-existant command or have a typo in a command, like so:

```
blarg.
```

It's not the best descriptive message, but it's better than what it did before.
Merge pull request #420 from Dunbaratu/fixes-417-error-on-nonexistent-function

Fixes 417. Error now shows on nonexstent function.