Set csingle->type in do_compile_modgroup

So its accessible to later code
Make "add_child" O(1) instead of O(N)
Fix use of add_to_modcallable()

it should just add.  It shouldn't create the parent
Move load-time removal of 'if' conditions

To where they make sense.  Which now also lets us do load-time
optimizations for:

	if (1) {

	}
	else {
		# no need to compile this
	}

and

	if (0) {
		# ignored
	}
	elsif (..) {
		# compiled
	}

Which didn't work before