open-uri: accept :open_timeout option

* lib/open-uri.rb (OpenURI::Options): add :open_timeout default
* (def OpenURI.open_http): check :open_timeout option
* (module OpenURI): rdoc for :open_timeout
* test/open-uri/test_open-uri.rb (test_open_timeout): new test
  [Feature #10361]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47869 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-10-11

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47870 b2dd03c8-39d4-4d8f-98ff-823fe69b080e