brew doctor - add check for non-standard X11
brew doctor - add check for non-standard X11

XQuartz is not known to work with Homebrew, though if you have it working
on your machine let us know.

rwhogg/brew,hanxue/linuxbrew,sjackman/homebrew,AnastasiaSulyagina/brew,AnastasiaSulyagina/brew,Linuxbrew/brew,AnastasiaSulyagina/brew,aw1621107/brew,mahori/brew,staticfloat/brew,vitorgalvao/brew,gregory-nisbet/brew,mgrimes/brew,rwhogg/brew,MikeMcQuaid/brew,palxex/brew,vitorgalvao/brew,jmsundar/brew,staticfloat/brew,vitorgalvao/brew,tonyg/homebrew,DomT4/brew,rwhogg/brew,bfontaine/brew,MikeMcQuaid/brew,amar-laksh/brew_sudo,gregory-nisbet/brew,ilovezfs/brew,toonetown/homebrew,muellermartin/dist,alyssais/brew,Homebrew/brew,EricFromCanada/brew,reelsense/brew,konqui/brew,mahori/brew,konqui/brew,zmwangx/brew,Linuxbrew/brew,konqui/brew,hanxue/linuxbrew,aw1621107/brew,mahori/brew,DomT4/brew,pseudocody/brew,muellermartin/dist,konqui/brew,JCount/brew,claui/brew,mistydemeo/homebrew,zmwangx/brew,nandub/brew,maxim-belkin/brew,zmwangx/brew,toonetown/homebrew,reitermarkus/brew,mistydemeo/homebrew,amar-laksh/brew_sudo,EricFromCanada/brew,mgrimes/brew,pseudocody/brew,tonyg/homebrew,palxex/brew,mgrimes/brew,hanxue/linuxbrew,toonetown/homebrew,sjackman/homebrew,JCount/brew,staticfloat/brew,bfontaine/brew,EricFromCanada/brew,JCount/brew,DomT4/brew,sjackman/homebrew,Homebrew/brew,claui/brew,Linuxbrew/brew,alyssais/brew,ilovezfs/brew,pseudocody/brew,EricFromCanada/brew,palxex/brew,gordonmcshane/homebrew,mistydemeo/homebrew,nandub/brew,Linuxbrew/brew,nandub/brew,maxim-belkin/brew,aw1621107/brew,maxim-belkin/brew,muellermartin/dist,ilovezfs/brew,Homebrew/brew,amar-laksh/brew_sudo,sjackman/homebrew,jmsundar/brew,reitermarkus/brew,JCount/brew,mahori/brew,gordonmcshane/homebrew,gregory-nisbet/brew,MikeMcQuaid/brew,nandub/brew,gordonmcshane/homebrew,claui/brew,DomT4/brew,claui/brew,vitorgalvao/brew,reelsense/brew,reelsense/brew,tonyg/homebrew,reitermarkus/brew,reitermarkus/brew,Homebrew/brew,alyssais/brew,jmsundar/brew,MikeMcQuaid/brew,bfontaine/brew