Add Python implementation of Object.connect_data()

Add GObject.Object.connect_data() which takes an optional "connect_flags"
keyword argument accepting GObject.ConnectFlags enum values. This is
for supporting user data swapping (ConnectFlags.SWAPPED).

https://bugzilla.gnome.org/show_bug.cgi?id=701843
tests: Add tests for connect_object()

Add tests for both introspected and non-introspected signals making use
of connect_object() and connect_object_after() in combination with GObject
and Python object swap data.

https://bugzilla.gnome.org/show_bug.cgi?id=727004
Add deprecation warning for connect_object() with non-GObject argument

GObject.connect_object() accepts any Python object and holds a strong
reference to it in the closure defeating the purpose of connect_object().
Add a warning so we can eventually limit connect_object() to GObject arguments
use the underlying g_signal_connect_object() which holds a weak reference.

https://bugzilla.gnome.org/show_bug.cgi?id=688064
Use AttributeError for static binding protection

Replace usage of RuntimeError with AttributeError in the dummy module
protecting importing of static bindings. This is needed so we don't break
modules like inspect which is used by ipython.
tests: Update tests for static binding protection to check AttributeErrors
Remove ffi wrapped destroy notify used for closure cleanup

Remove global ffi wrapper for _pygi_invoke_closure_free() and instead use
a pointer to _pygi_invoke_closure_free() directly. There is no need to wrap
a known single use function with an ffi closure. Originally introduced in
commit 610dd1eec87f.
tests: Silence valgrindlog and valgrindxml output from forked procs

This is needed to properly diff valgrind runs between commits.
Fix invalid unref after getting callable container

Don't unref the results of g_base_info_get_container() because it is
transfer-none. This was causing an attempted unref on an invalid object
when setting up callback caches for signals.

https://bugzilla.gnome.org/show_bug.cgi?id=727004
release 3.13.4
configure.ac: post release version bump to 3.13.5