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.
During an npm-link command it will let the installer know that the install script is aware of the state it has just been put in, that it doesn't have to do anything, just let npm link to the folder.