Fixing install.js when npm link is called.

Currently npm link calls install.js but provides it with a bad path as several files that being with "phantomjs" exit in the npm root folder (for global calls). Therfore, "which" incorrectly resolves the path, giving a mistaken path to the promise. A simple check to make sure that the path isn't resolving "phantomjs" immediately after "npm" clears up the issue nicely (i.e. the path does not contain the substring "npm/phantomjs", as the correct file will always exit within node_modules of the npm folder. If the culprit substring isn't present the file writes, if it is, it doesn't.
Can you comment what this line means for future reference.  There are lots of edge cases so its important to document for future spelunking.