be stricter about checking googledrive revisions
be stricter about checking googledrive revisions

 * Use a whitelist to determine who is allowed to request revisions,
   instead of a blacklist.  While 'reader' and 'commenter' roles are
   definitely not allowed to list revisions, it appears that there are
   unknown other roles with the same restriction.  Start requiring the
   user to be an owner to list revisions.

rdhyee/waterbutler,RCOSDP/waterbutler,felliott/waterbutler,TomBaxter/waterbutler,CenterForOpenScience/waterbutler,Johnetordoff/waterbutler