Fix MacOS::CLT.installed? for 10.9+
Fix MacOS::CLT.installed? for 10.9+

This continues to use mavericks_dev_tools? instead of trying to read
from pkgutil because pkgutil is really slow.

Fixes Homebrew/homebrew#24123.

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