Recently in #2451 we disallowed bip32 derivation paths with the leading
'm' variable.
There is some confusion as to what exactly the bip specifies however
Bitcoin Core RPC call `getaddressinfo` returns a derivation path with a
leading "m/". This means we need to be able to parse it irrespective of
what the bip says.
Be more liberal in what we accept as a derivation path, including both
with and without the leading 'm/'.
Leave the full investigation of the bip to a later date.
Change back some of the test strings as makes sense and include test
strings to showcase the full current behaviour.
830c1e9cfe