Add Go language module, resources

This introduces a new GoResource category of resource. GoResources
have a specialized stage method which allows a resource to stage
itself into a gopath.

The new Go language module provides a one-liner to stage all
GoResources present in the formula.

Library/Homebrew/formula.rb

@@ -660,12 +660,16 @@ class Formula
     end
 
     # Define a named resource using a SoftwareSpec style block
-    def resource name, &block
+    def resource name, klass=Resource, &block
       specs.each do |spec|
-        spec.resource(name, &block) unless spec.resource_defined?(name)
+        spec.resource(name, klass, &block) unless spec.resource_defined?(name)
       end
     end
 
+    def go_resource name, &block
+      resource name, Resource::Go, &block
+    end
+
     def depends_on dep
       specs.each { |spec| spec.depends_on(dep) }
     end

Library/Homebrew/language/go.rb

+require "resource"
+
+module Language
+  module Go
+    # Given a set of resources, stages them to a gopath for
+    # building go software.
+    # The resource names should be the import name of the package,
+    # e.g. `resource "github.com/foo/bar"`
+    def self.stage_deps resources, target
+      godeps = resources.grep(Resource::Go)
+      godeps.each {|resource| resource.stage target}
+    end
+  end
+end

Library/Homebrew/resource.rb

@@ -130,4 +130,10 @@ class Resource
       raise TypeError, "version '#{val.inspect}' should be a string"
     end
   end
+
+  class Go < Resource
+    def stage target
+      super(target/name)
+    end
+  end
 end

Library/Homebrew/software_spec.rb

@@ -69,10 +69,10 @@ class SoftwareSpec
     resources.has_key?(name)
   end
 
-  def resource name, &block
+  def resource name, klass=Resource, &block
     if block_given?
       raise DuplicateResourceError.new(name) if resource_defined?(name)
-      res = Resource.new(name, &block)
+      res = klass.new(name, &block)
       resources[name] = res
       dependency_collector.add(res)
     else