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@42927 b2dd03c8-39d4-4d8f-98ff-823fe69b080e