vm_method.c: rb_method_entry_at

* vm_method.c (rb_method_entry_at): return the method entry for id at
  klass, without ancestors.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40683 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
proc.c: Kernel#singleton_method

* proc.c (rb_obj_singleton_method): new method Kernel#singleton_method
  which returns a Method object of the singleton method.
  non-singleton method causes NameError, but not aliased or zsuper
  method, right now.
  [ruby-core:54914] [Feature #8391]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40684 b2dd03c8-39d4-4d8f-98ff-823fe69b080e