merge revision(s) r46368,r46371: [Backport #9913]

	* ext/digest/digest.c (rb_digest_instance_equal):
	  fix #== for non-string arguments. [ruby-core:62967] [Bug #9913]

	* test/digest/test_digest.rb: add test for above.

	* ext/digest/digest.c (rb_digest_instance_equal): no need to call
	  `to_s` twice.  [Bug #9913]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@46809 b2dd03c8-39d4-4d8f-98ff-823fe69b080e