XCB: grey scale output support
XCB: grey scale output support

There is a problem with blending GREY on GREY though.
Use `Xephyr -grayscale` to test.

xkfz007/vlc,jomanmuk/vlc-2.1,jomanmuk/vlc-2.2,xkfz007/vlc,krichter722/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc-2.1,shyamalschandra/vlc,vlc-mirror/vlc-2.1,krichter722/vlc,shyamalschandra/vlc,krichter722/vlc,krichter722/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,jomanmuk/vlc-2.1,jomanmuk/vlc-2.1,shyamalschandra/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.2,shyamalschandra/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,xkfz007/vlc,krichter722/vlc,vlc-mirror/vlc,vlc-mirror/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,shyamalschandra/vlc,xkfz007/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.2,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.1,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,krichter722/vlc,krichter722/vlc,vlc-mirror/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.1,vlc-mirror/vlc-2.1,vlc-mirror/vlc