This is the normal case: you only want to reserve inputs which
are not already reserved. This saves you iterating through the
results and unreserving some if you weren't exclusive.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
reserveinputs marks UTXOs reserved for 12 hours, so we won't select them
for spending: unreserveinputs marks them available again.
Exposes param_psbt() for wider use.
Disabled the test_sign_and_send_psbt since we're altering the API;
the final patch restores it.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>