The PAM module uses dbus-glib, static gobject types, etc,
so it really can't get unloaded.
This commit adds some linker-fu to keep it resident even
after the pam module closes.
- Use D-Bus native properties instead of a GetProperties call.
- Fix a number of front-ends by registering the right signals and
marshallers following the "done" signal argument addition
- Fix VerifyStart call in the pam module
