* lib/rubygems: Import RubyGems 2.1.0 Release Candidate

* test/rubygems:  ditto.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42693 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rubygems/commands/build_command.rb

@@ -15,6 +15,25 @@ class Gem::Commands::BuildCommand < Gem::Command
     "GEMSPEC_FILE  gemspec file name to build a gem for"
   end
 
+  def description # :nodoc:
+    <<-EOF
+The build command allows you to create a gem from a ruby gemspec.
+
+The best way to build a gem is to use a Rakefile and the Gem::PackageTask
+which ships with RubyGems.
+
+The gemspec can either be created by hand or extracted from an existing gem
+with gem spec:
+
+  $ gem unpack my_gem-1.0.gem
+  Unpacked gem: '.../my_gem-1.0'
+  $ gem spec my_gem-1.0.gem --ruby > my_gem-1.0/my_gem-1.0.gemspec
+  $ cd my_gem-1.0
+  [edit gem contents]
+  $ gem build my_gem-1.0.gemspec
+    EOF
+  end
+
   def usage # :nodoc:
     "#{program_name} GEMSPEC_FILE"
   end