Typechecker should not check argument types after it finds incorrect # of params

[marijnh]

Right now, if you forget a parameter, you first get an error about the wrong number of parameters, and then more errors about the mismatched types of the parameters you provided.

[msullivan]

It is important to still typecheck the argument expressions, or else the compiler fails with an internal error when it finds an expression without a type in the type table. That doesn't mean we need to check against the arguments, though. Anyways, I'll take this.