This is required for VLS which wants to know (and potentially decline) invoices
we're trying to pay.
As a nice side effect, our "check" command for xpay now does much more thorough
checking of arguments.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Any file in this directory which is executable and whose name only
consists of alphanumeric characters, space, '.', '-' or '_' will be
automatically loaded when lightningd starts (unless suppressed with
commandline options).