More Bugfixes

1. Fix instances where typechecking would not terminate when dealing with classes in some hierarchy
2. Miscellaneous IRBuilder fixes
3. Constructor arguments are now in scope in the superclass call, eg. this is now possible:

class Foo : Bar
{
    init(x: int, y: int) : super(x * y) { ... }
}

4. Fix issues where methods could not be called on rvalues, eg. Foo().bar(...)
5. Fix dumb issue where omitting optional arguments would hard crash the compiler