patch: add support for changing directory

Library/Homebrew/patch.rb

@@ -135,7 +135,7 @@ class ExternalPatch
   end
 
   def apply
-    dir = Pathname.pwd
+    base_dir = Pathname.pwd
     resource.unpack do
       patch_dir = Pathname.pwd
       if patch_files.empty?
@@ -149,6 +149,8 @@ class ExternalPatch
 
         patch_files << children.first.basename
       end
+      dir = base_dir
+      dir /= resource.directory if resource.directory.present?
       dir.cd do
         patch_files.each do |patch_file|
           ohai "Applying #{patch_file}"

Library/Homebrew/resource.rb

@@ -198,6 +198,7 @@ class Resource
 
     def initialize(&block)
       @patch_files = []
+      @directory = nil
       super "patch", &block
     end
 
@@ -206,6 +207,12 @@ class Resource
       @patch_files.concat(paths)
       @patch_files.uniq!
     end
+
+    def directory(val = nil)
+      return @directory if val.nil?
+
+      @directory = val
+    end
   end
 end