Compatibly renamed Gem::DependencyResolver to Gem::Resolver.

  Added support for git gems in gem.deps.rb and Gemfile.

  Fixed resolver bugs.

* test/rubygems: ditto.

* lib/rubygems/LICENSE.txt:  Updated to license from RubyGems trunk.
  [ruby-trunk - Bug #9086]

* lib/rubygems/commands/which_command.rb:  RubyGems now indicates
  failure when any file is missing.  [ruby-trunk - Bug #9004]

* lib/rubygems/ext/builder:  Extensions are now installed into the
  extension install directory and the first directory in the require
  path from the gem.  This allows backwards compatibility with msgpack
  and other gems that calculate full require paths.
  [ruby-trunk - Bug #9106]



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43714 b2dd03c8-39d4-4d8f-98ff-823fe69b080e