Added methods to handle error replies from the POST requests. Google
returns error messages in the <batch> tag for each error in creation of
an entry. These replies are not documented anywhere, so just checking
for the string "Error" in the title of the entry feed. With this patch,
slow sync between device and server works fine. Next step is to check
the fast sync scenarios

Signed-off-by: Sateesh Kavuri <sateesh@mobilitas.co>