Proposed patch

Hi,

Seems that we do not need our version of gdk_cairo_reset_clip, also I am
not sure if it is really safe to use cairo_reset_clip in
GR_UnixCairoGraphics::saveRectangle() and
GR_UnixCairoGraphics::restoreRectangle().

Attached patch cleans things but I'd like it to be reviewed because of
the above. Also, it seems that the definition of GTK_CHECK_VERSION is
not needed but I don't understand how gtk.h is included, so I didn't
remove it.

Cheers,
Jean