[oe] Adding support for DirectFB across the board

[shanevolpe at gmail.com]

All,
I have been adding in support for directFB to as many packages as
possible, however one issue I have ran into several times is what do I
do when there are packages that can be compiled with X11 or directfb
support and then what do you do with packages that may depend on a
package compiled with directfb or X11.  Ok that was pretty confusing,
let me give an example.

I have added cairo-directfb which compiles cairo with directfb instead
of X11.  Next I wanted to add (update) gtk+-directfb to use
cairo-directfb instead of cairo.  That part was easy I just changed
the DEPENDS cairo in gtk+-directfb to cairo-directfb..  The issue came
when I noticed that gtk+ also requires pango which requires cairo so
what do I do here, do I make a new pango called pango-directfb?  It
seems like the better thing would be set up a virtual/cairo and set it
to either cairo or cairo-directfb.  If I go that route how do I set it
up so it does not break everyone's build that does not have
virtual/cairo set, is there a way to default it to something like
cairo?
Regards,
Shane