Changes to allow token storage to work after App Engine Datastore changed it so that
nested structs could no longer be stored.

Got the idea for how to fix this here: http://blog.sohjsolwin.com/2013/10/helpouts-meetups-and-mirror-qucikstart.html
Changes Suggested in PR

Moved struct from main.go to util.go and moved error handling from
util.go to auth.go
fixed error message
ran it through go fmt
Merge pull request #7 from andrewwatson/master

Changes to allow token storage to work after App Engine Datastore change...