Fixed installing platform gems
Restored concurrent requires
Fixed installing gems with extensions with --install-dir
Fixed `gem fetch -v` to install the latest version
Fixed installing gems with "./" in their files entries
* test/rubygems/test_gem_package.rb: Tests for the above.
* NEWS: Updated for RubyGems 2.1.3
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42938 b2dd03c8-39d4-4d8f-98ff-823fe69b080e