merge revision(s) 45057,45059: [Backport #9533]

	* hash.c (rb_hash_flatten): fix behavior of flatten(-1).
	  [ruby-dev:47988] [Bug #9533]

	* test/ruby/test_array.rb: test for above.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@45126 b2dd03c8-39d4-4d8f-98ff-823fe69b080e