Don't use doctest syntax in docstrings for examples

These are not actual doctests, so don't use the >>> syntax there. Just indent
them.

This fixes pyflakes 0.7 failures.

https://bugzilla.gnome.org/show_bug.cgi?id=701009
Re-add support for passing GValue's by reference

Fix special casing when marshaling from a Python held GValue
to a GValue argument intended for a function call.
The re-factoring of GValue marshaling in commit #9e47afe459df942d9f
broke this by always making a copy of the GValue. This removed the
ability to retrieve values with functions like
gtk_style_context_get_style_property.

https://bugzilla.gnome.org/show_bug.cgi?id=701058
Clear return value of closures to zero when an exception occures

For return types other than void, set the ffi closure return argument
to 0 when a Python exception occures. This a good default in general
but also has the side affect of fixing failing idle callbacks
by causing them to be removed from main loops (after their stack
is printed).

https://bugzilla.gnome.org/show_bug.cgi?id=702552
gi/pygi-info.c: Avoid C99-style variable declaration

https://bugzilla.gnome.org/show_bug.cgi?id=702786
pygtkcompat: Fix for missing methods on Windows

Deal with non-existing Gtk.Clipboard.get() and
GdkPixbuf.Pixbuf.new_from_file_at_scale() methods.

https://bugzilla.gnome.org/show_bug.cgi?id=702787
Add marshalling of GI_TYPE_TAG_VOID held in a GValue to int

Replace assertion for this case with a simple marshalling of the
pointer value to a Python int. While not particularly useful
this allows some callbacks in WebKit to function without causing
a segfault.

https://bugzilla.gnome.org/show_bug.cgi?id=694233
examples/option.py: Port to GI and Python 3
release 3.8.3
testhelper: Fix import requirement for GObject

Replace the importing of gi._gobject._gobject with gi.repository.GObject
in tests/testhelpermodule.c

The testhelper module was only importing the static bindings
(gi._gobject._gobject) and not the overrides (gi.repository.GObject).
This was causing some tests to fail when test_thread was the first
test to run in the suite due to it registering new types based on
PyGObject_Type.

https://bugzilla.gnome.org/show_bug.cgi?id=703647