Allow include before calling Module#initialize

	This is to allow Module subclasses that include modules before
	calling super in the subclass's initialize.

	Remove rb_module_check_initializable from Module#initialize.
	Module#initialize only calls module_exec if a block is passed,
	it doesn't have other issues that would cause problems if
	called multiple times or with an already initialized module.

	Move initialization of super to Module#allocate, though I'm not
	sure it is required there.  However, it's needed to be removed
	from Module#initialize for this to work.

	Fixes [Bug #18292]
	---
	 class.c                  |  1 +
	 object.c                 |  1 -
	 test/ruby/test_module.rb | 10 ++++++++++
	 3 files changed, 11 insertions(+), 1 deletion(-)