Const declarations aren't typechecked

[jruderman]

const i: str = 10;
fn main() { log i; }

Should give an error in typeck, but instead it gets to LLVM, which says

Assertion failed: (InitVal->getType() == getType()->getElementType() && "Initializer type must match GlobalVariable type"), function setInitializer, file Globals.cpp, line 168.