This allows GDB to print values, but also allows us to use them in
'case' statements. This wasn't allowed before because they're not
constant terms.
This also made it clear there's a clash between two error codes,
so move one.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Changed: JSON-RPC: Error code from bcli plugin changed from 400 to 500.