AU: Try delta updates first, then full updates

Also, some bug fixes.

Review URL: http://codereview.chromium.org/492008
diff --git a/omaha_response_handler_action.cc b/omaha_response_handler_action.cc
index 0a8472e..0a0a660 100644
--- a/omaha_response_handler_action.cc
+++ b/omaha_response_handler_action.cc
@@ -22,6 +22,7 @@
   ScopedActionCompleter completer(processor_, this);
   const UpdateCheckResponse& response = GetInputObject();
   if (!response.update_exists) {
+    got_no_update_response_ = true;
     LOG(INFO) << "There are no updates. Aborting.";
     return;
   }
@@ -47,7 +48,8 @@
     filename.resize(255);
   }
   // TODO(adlr): come up with a better place to download to:
-  install_plan.download_path = utils::kStatefulPartition + "/" + filename;
+  install_plan.download_path = string(utils::kStatefulPartition) + "/" +
+      filename;
   if (HasOutputPipe())
     SetOutputObject(install_plan);
   LOG(INFO) << "Using this install plan:";