AU: Changes for deltas on traditional bios machines.

BUG=None
TEST=Attached unittests/tested on image

- Fix uninitialized variable err in action processor unittest

- Let Omaha dictate if an update is a delta or full update

- Bug fix in delta generator for differently-sized images

- More logging when applying delta updates

- Fix infinite loop in http fetcher unittest

- log each HTTP connection to know when a dropped connection is
  reestablished.

- Detect when speed goes below a threshold and reestablish HTTP
  connection (currently < 10bytes/sec for 90 contiguous seconds).

- Fix stack overflow in libcurl http fetcher.

- optimize out a lot of needless CPU usage in libcurl http fetcher
  (turns out adding a glib main loop source uses a lot of CPU).

- subprocess: pass PATH, log stdout/stderr

- postinstall runner: support for ext3 and ext4 target filesystems.

Review URL: http://codereview.chromium.org/2805027
diff --git a/omaha_response_handler_action_unittest.cc b/omaha_response_handler_action_unittest.cc
index 489d5e7..f751bbe 100644
--- a/omaha_response_handler_action_unittest.cc
+++ b/omaha_response_handler_action_unittest.cc
@@ -88,6 +88,7 @@
     in.size = 12;
     in.needs_admin = true;
     in.prompt = false;
+    in.is_delta = false;
     InstallPlan install_plan;
     EXPECT_TRUE(DoTest(in, "/dev/sda3", &install_plan));
     EXPECT_TRUE(install_plan.is_full_update);
@@ -105,9 +106,10 @@
     in.size = 12;
     in.needs_admin = true;
     in.prompt = true;
+    in.is_delta = true;
     InstallPlan install_plan;
     EXPECT_TRUE(DoTest(in, "/dev/sda5", &install_plan));
-    EXPECT_TRUE(install_plan.is_full_update);
+    EXPECT_FALSE(install_plan.is_full_update);
     EXPECT_EQ(in.codebase, install_plan.download_url);
     EXPECT_EQ(in.hash, install_plan.download_hash);
     EXPECT_EQ("/dev/sda3", install_plan.install_path);
@@ -122,6 +124,7 @@
     in.size = 12;
     in.needs_admin = true;
     in.prompt = true;
+    in.is_delta = false;
     InstallPlan install_plan;
     EXPECT_TRUE(DoTest(in, "/dev/sda3", &install_plan));
     EXPECT_TRUE(install_plan.is_full_update);