Allow partial installation of resources

Library/Homebrew/extend/pathname.rb

@@ -1,5 +1,6 @@
 require 'pathname'
 require 'mach'
+require 'resource'
 
 # we enhance pathname to make our code more readable
 class Pathname
@@ -12,6 +13,8 @@ class Pathname
       case src
       when Resource
         src.stage(self)
+      when Resource::Partial
+        src.resource.stage { install(*src.files) }
       when Array
         if src.empty?
           opoo "tried to install empty array to #{self}"

Library/Homebrew/resource.rb

@@ -62,6 +62,12 @@ class Resource
     end
   end
 
+  Partial = Struct.new(:resource, :files)
+
+  def files(*files)
+    Partial.new(self, files)
+  end
+
   # For brew-fetch and others.
   def fetch
     # Ensure the cache exists