Import gemspec and test file from ruby/webrick.

  * webrick.gemspec: Update files and dependency for standalone gem.
  * test/webrick/utils.rb: Added explicitly loading of EnvUtil for
    test suite without ruby core test suite.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58473 b2dd03c8-39d4-4d8f-98ff-823fe69b080e