Add rb_define_class_id_under to the C API and update rb_define_class_under to raise a TypeError for a superclass mismatch

[yorickpeterse]

This function is the same as rb_define_class_under except the name should be an ID instead of a const char *.

[yorickpeterse]

From the 2.3 changelog:

rb_define_class_id_under() now raises a TypeError exception when the class is already defined but its superclass does not match the given superclass, as well as definitions in ruby level.

[yorickpeterse]

@ahmadsherif Does our rb_define_class_id_under / rb_define_class_under raise TypeError in the case mentioned above?

[ahmadsherif]

@yorickpeterse It does through rubinius::Helpers::open_class which in turn calls rubinius::Helpers::check_superclass.

[yorickpeterse]

@ahmadsherif Ah OK. Thanks for looking into this!