Hybrid symlink approach for Mavericks launcher issue

This approach should ensure that SSBs will continue to track Chrome updates as the launcher included in the real Google Chrome app folder is updated.  Saves a symlink to the location of the real executable at SSB creation time, and recopies at launch in case any Chrome updates were applied in the interim.  The small size of the executable should make this copy negligible (could probably do an rsync to avoid unnecessary copies, but I'm not sure if we can assume rsync is available across all relevant versions of OS X).