Return WP_Error instead of array of empty objects for a revisions permissions error
Merge branch 'bugfix/properly-handle-revision-perms-error' of git://github.com/tlovett1/WP-API into tlovett1-bugfix/properly-handle-revision-perms-error
Renamed permission check variable in get_revisions method to parent.
Added detail to permission check error message in get_revisions method.
Merge pull request #276 from WP-API/tlovett1-bugfix/properly-handle-revision-perms-error

Return WP_Error instead of array of empty objects for a revisions permissions error.  Closes #276 and #251.