X11Requirement: Check xdpyinfo if Xorg fails [Linux] (#581)
X11Requirement: Check xdpyinfo if Xorg fails [Linux] (#581)

Xorg -version fails if the user does not have console ownership.

Fix the error:
$ Xorg -version
Fatal server error:
PAM authentication failed, cannot start X server.
Perhaps you do not have console ownership?

Fixes https://github.com/Linuxbrew/brew/issues/580
hanxue/linuxbrew,hanxue/linuxbrew,Linuxbrew/brew,Linuxbrew/brew,Linuxbrew/brew,maxim-belkin/brew,maxim-belkin/brew,Linuxbrew/brew,hanxue/linuxbrew,maxim-belkin/brew