We were automatically falling back to bolt12 decoding, clobbering the
fail message. Ultimately resulting in confusing error
messages (expected prefix lni but got lnbtrc). Now we first determine
which decoding we're trying to do, and then only decode accordingly.
Changelog-Fixed: pay: Report the correct decoding error if bolt11 parsing fails.
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).