directfb: bump version

Closes #379

update DirectFB to version 1.4.0

A new stable version of DirectFB has been released upstream,
http://directfb.org/index.php?path=Main%2FNews&entry=2009-06-04-1.niels



Attached patch updates the DirectFB package and introduces a BR2
configuration option for the RGB16 dithering feature that is new in
DirectFB 1.4.0.

Signed-off-by: Sven Neumann <s.neumann@raumfeld.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>