hash.c: support key swapping in Hash#transform_keys!
* hash.c (rb_hash_transform_keys_bang): support key swapping in
Hash#transform_keys!
[Bug #14380] [ruby-core:84951]
* test/ruby/test_hash.rb (test_transform_keys_bang):
add assertions for this change
Fix rubyspec against the change in Hash#transform_keys!
[Bug #14380] [ruby-core:84951]
merge revision(s) 62042,62044: [Backport #14380]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@62889 b2dd03c8-39d4-4d8f-98ff-823fe69b080e