[K42-discussion] Sync service is now on by default.

[Dilma DaSilva]

The default behavior now in k42 is to have an update daemon running
to flush file data from the FCMs to the file system. Our previous way
was flushing a file to the file system on close().

It's possible to run with the old behavior, i.e., no update daemon
with flush happening on close. You can do this by turning on the
control flag BOOT_WITHOUT_SYNC_SERVICE, and then doing a
soft-reboot.

Remember to issue a "sync" operation if there is file data you want
to have propagated to the file system before you reboot or before
the system crashes. The sync will block until the file dirty
pages are propagated to disk.

Dilma