Some things were odd with regard to the ownership of passed objects. Try
to make things sane overall, in particular with the possible floating
FpPrint reference.
We prefixed them with fp- which is not as obvious as fpi-. Also,
explicitly mark them as private and to be skipped in the GObject
Introspection annotatinos.
Warning: FPrint: (Signal)fp-image-device-state-changed: argument object: Unresolved type: 'FpiImageDeviceState'
