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_request_action.h b/omaha_request_action.h
index 0f066e3..307798b 100644
--- a/omaha_request_action.h
+++ b/omaha_request_action.h
@@ -42,6 +42,7 @@
   off_t size;
   bool needs_admin;
   bool prompt;
+  bool is_delta;
 };
 COMPILE_ASSERT(sizeof(off_t) == 8, off_t_not_64bit);