go back to the original way in #184 of detecting phantomjs global install

Hello @dpup, 

Please review the following commits I made in branch 'nick-back'.

8ccfdcb345c5faa2f9b76bddfa2c983dacb717be (2014-07-09 18:47:28 -0400)
go back to the original way in #184 of detecting phantomjs global install

R=@dpup