AU: Class to perform delta updates.

A class to perform delta updates and the associated unittests. Also,
change the delta diff generator executable to be able to apply a
delta, which is handy for debugging.

TEST=Attached unit test, hand-tested on real build images
BUG=552

Review URL: http://codereview.chromium.org/1718001
diff --git a/filesystem_copier_action.cc b/filesystem_copier_action.cc
index f9b6869..2a361ee 100644
--- a/filesystem_copier_action.cc
+++ b/filesystem_copier_action.cc
@@ -93,7 +93,7 @@
 bool FilesystemCopierAction::Mount(const string& device,
                                    const string& mountpoint) {
   CHECK(!is_mounted_);
-  if(utils::MountFilesystem(device, mountpoint))
+  if(utils::MountFilesystem(device, mountpoint, 0))
     is_mounted_ = true;
   return is_mounted_;
 }