config/graphic: enable Composite support if build with Nouveau GPU drivers, add some comments

Signed-off-by: Stephan Raue <stephan@openelec.tv>
Merge branch 'master' of github.com:OpenELEC/OpenELEC.tv
Merge branch 'master' of github.com:OpenELEC/OpenELEC.tv
Mesa: update to Mesa-10.0.0-rc2

Signed-off-by: Stephan Raue <stephan@openelec.tv>
libdrm: update to libdrm-2.4.49

Signed-off-by: Stephan Raue <stephan@openelec.tv>