Rework -L logic to use the idiom used in handling the leases file.

Rework -L logic to use the idiom used in handling the leases file.
i.e. open FILE during program set up and use the FILE created for
the rest of the program lifetime after dropping privilege and
pledge()'ing. No need for passing messages to the priv process.

Tweak lease file handling a bit in passing.

Monitoring the -L file with external programs like sysutils/entr
still works.

Looks good to sthen@.