When accessing a shared folder, the folder's owner appears as mountpoint
but wasn't wrapped by a quota storage wrapper.
This fix makes sure that all home storages are wrapped by a quota
storage wrapper, if applicable, to make sure quotas are respected when
uploading into shared folders.
instanceid is generated by uniqid() and then used as the
session_name. Because session_name requires at least one letter
and uniqid() does not guarantee to provide that, in the case that
uniqid() generates a string of only digits, the user will be stuck
in an infinite login loop because every request will generate a
new PHP session.
