* lib/tmpdir.rb (Dir.mktmpdir): Accept nil again, as Ruby 2.1.
  [ruby-core:66943] [Bug #10616] Fixed by Alex Slynko.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48905 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Add a test for Dir.mktmpdir(nil) [ruby-core:66943] [Bug #10616].


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48906 b2dd03c8-39d4-4d8f-98ff-823fe69b080e