[PATCH] allow undef as argument in a few functions

[Quentin Sculo <squentin free fr>]

Hi,
I was annoyed some time ago (but didn't report it) that
$gdkwindow->draw_pixbuf didn't accept undef for the gc argument, even
though the C function allows NULL [1], here's a fix, as well as a few
similar cases I found.
I haven't looked at all functions, so there are most likely other cases.
Don't hesitate to mention those you might have noticed, I can make
patches for them.

Quentin

[1]
http://library.gnome.org/devel/gdk/unstable/gdk-Drawing-Primitives.html#gdk-draw-pixbuf

Attachment: 0001-GdkDrawable-allow-undef-as-argument-in-3-methods.patch
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Attachment: 0002-GtkWidget-allow-undef-as-argument-in-2-methods.patch
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Attachment: 0003-GdkWindow-allow-undef-as-argument-in-6-methods.patch
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