Wrong mode for main() argument causes LLVM assertion failure

[catamorphism]

fn main(+_args: ~[~str]) {}

results in:

Assertion failed: ((i >= FTy->getNumParams() || FTy->getParamType(i) == Args[i]->getType()) && "Calling a function with a bad signature!"), function init, file /Users/tchevalier/rust/src/llvm/lib/VMCore/Instructions.cpp, line 280.

I know modes are going away, but in general it's probably worth testing that doing various weird things to main's signature yields a proper error.

[catamorphism]

Meh, modes are gone and I am unmotivated to add more tests for this at the moment :-)