[Graphics] More convenient backend access

[John W. Eaton]

On 24-Jan-2008, Michael Goffioul wrote:

| The attached patch allows a more convenient backend access from any
| graphics_object (by delegating to the parent object). It's not heavily
| used for the moment, but I'm sure it'll be convenient for future development.
| 
| Michael.
| 
| src/ChangeLog
| 
| 2008-01-23  Michael Goffioul <michael.goffioul at gmail.com>
| 
|     * graphics.h.in (base_properties::get_backend,
|     base_graphics_object::get_backend, graphics_backend::get_backend):
|     New methods for convenient access to the backend.
|     (figure::get_backend, figure::set_backend): Remove.
|     * graphics.cc (base_properties::get_backend): New method.
|     (Fdrawnow): Use graphics_object::get_backend to simplify code.

I applied this patch and checked it in.

Thanks,

jwe