main: replace paniclog with logger(1)
main: replace paniclog with logger(1)

Instead of redirecting stdout and stderr to /tmp/gocryptfs_paniclog,
where it is hard to find, redirect them to a newly spawned logger(1)
instance that forwards the messages to syslog.

See https://github.com/rfjakob/gocryptfs/issues/109 for an example
where the paniclog was lost due to a reboot.

Also, instead of closing stdin, redirect it to /dev/null, like most
daemons seem to do.

rfjakob/gocryptfs,rfjakob/gocryptfs,davesteele/gocryptfs,davesteele/gocryptfs,davesteele/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs