CVE-2015-3900. * lib/rubygems/remote_fetcher.rb: ditto. * test/rubygems/test_gem_remote_fetcher.rb: added testcase for CVE-2015-3900 git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50829 b2dd03c8-39d4-4d8f-98ff-823fe69b080e