Add spec examples for Module#method_added
Add specs for {Kernel|BasicObject}#singleton_method_added
Fix Module#alias_method for hooking method added
Simplify to check singleton class

refer: https://github.com/rubinius/rubinius/pull/2368\#discussion_r4459063
Merge pull request #2368 from kachick/fix-module-alias_method_for_hooking_method_added

Module#alias_method should call {singleton_}method_added