semantics. now:
(1) dirty file systems will always be checked; nothing new there.
(2) if not '-f' clean file systems will _NEVER_ be checked,
i.e. they won't be checked even if -p isn't specified. This
allows one to 'fsck -p ; fsck' to preen, then clean up
anything that 'fsck -p' barfs on, without waiting for the
clean file systems to be checked again.
(3) if '-f' clean file systems will ALWAYS be checked. This
allows people to put 'fsck -fp' into /etc/rc on systems
where they're leery of the FS clean flag state, need
the extra reliability, and can afford time 'wasted'
in checks.
The assumption made here is that if a file system is marked clean, it
_IS CLEAN_, really, and shouldn't be checked unless fsck is explicitly
told to (with -f). This should be a valid assumption, but may not be in
the presence of file system bugs. Documentation updated to note '-f'.
