Mark all the methods on the device as async, so we
can get access to the associated DBusGMethodInvocation.
When claiming the device, remember the sender, and for every
API entry point, check that the sender is the same as the one
that made the original claim.
Trying to enroll a user whilst the device is already claimed
from another program will fail with:
** ERROR **: failed to claim device: Device was already claimed
This is the first step towards PolicyKit and multi-user support
This will be needed to get better error messages to
users of the D-Bus API. We use glib's builtin gettext
support. No strings marked as translatable yet, we'll
need to mark those user-visible strings carefully and
review them.
