#31 configure.in should use pkg-config for DirectFB

[Cristian Morales Vega]

The configure scripts has some hardcoded paths that aren't true in my system:
- If the user doesn't says otherwise, the default directfb_driver_dir should be taken from pkg-config. In my case it is /usr/lib64/directfb-1.2-0, and there is no directfb -> directfb-1.2-0 symlink.
- directfb.h is at "/usr/include/directfb", not "/usr/include/"
- directfb_version.h is also at "/usr/include/directfb", not "/usr/include/directfb-internal"