[Bugfix] Fix issue #10: Use of g_object_add_weak_pointer

Fix https://github.com/01org/dleyna-renderer/issues/10

Need to add weak pointer on GObject GUPnP Proxy when the proxy
is used in a function call issued from an API.

There are some cases, with async tasks and GCancellable, where proxies
could be freed while async task callbacks are not yet proceed.

Signed-off-by: Ludovic Ferrandis <ludovic.ferrandis@intel.com>
[Coding Guidelines] Fix issue #12: Make error strings single line

Fix https://github.com/01org/dleyna-renderer/issues/12

Fix also 2 checkpatch issues about parameters alignment.

Signed-off-by: Ludovic Ferrandis <ludovic.ferrandis@intel.com>