image->bpp set wrong in gdk_image_get

[Tor Lillqvist <tml sgic fi>]

I just noticed that in GTk+ 1.2, gdk_image_get sets image->bpp to the
bits-per-pixel value, even if it according to the comments in
gdktypes.h, and the other places where it is set, should be the
bytes-per-pixel value. (This is the reason why my wmf gimp plug-in
didn't work on X11...)

--tml