(Open3.popen_run): extracted from Open3.popen3.
(Open3.popen2): new method.
(Open3.popen2e): new method.
(Open3.pipeline_rw): new method.
(Open3.pipeline_r): new method.
(Open3.pipeline_w): new method.
(Open3.pipeline_run): new private method.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@20512 b2dd03c8-39d4-4d8f-98ff-823fe69b080e