merge revision(s) 6118e8a4, dc644482: [Backport #20716]

	Fix method caching bug when including/prepend module A that prepends module B

	Fix by always adding the generated iclass to the subclasses list,
	otherwise the method cache for the iclass is not cleared when
	the method in the module is overwritten.

	Fixes [Bug #20716]

	Remove an unused variable