Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Add some FEATURE macros for various GEOM classes.

No FreeBSD version bump, the userland application to query the features will
be committed last and can serve as an indication of the availablility if
needed.

Sponsored by: Google Summer of Code 2010
Submitted by: kibab
Reviewed by: silence on geom@ during 2 weeks
X-MFC after: to be determined in last commit with code from this project

Don't pass error value pointer to g_read_data(9) at all if we don't
have any use of it.

Suggested by: pjd

Check for g_read_data(9) errors properly:

o The only indication of error condition is NULL value returned by
the function;

o value pointed to by error argument is undefined in the case when
operation completes successfully.

Discussed with: phk

/* -> /*- for copyright notices, minor format tweaks as necessary

Tag all geom classes in the tree with a version number.

Use default method initialization on geoms.

Do not check error code from closing ->access() calls, we know they succeed.

Remove the absolute count g_access_abs() function since experience has
shown that it is not useful.

Rename the relative count g_access_rel() function to g_access(), only
the name has changed.

Change all g_access_rel() calls in our CVS tree to call g_access() instead.

Add an #ifndef BURN_BRIDGES #define of g_access_rel() for source
code compatibility.

Fix memory leak.

PR: kern/58634
Submitted by: le
Approved by: phk

Fix two old/new consumer confusions.

Submitted by: Pawel Jakub Dawidek <nick@garage.freebsd.pl>

Fix a braino memory leak.

Found by: Pawel Jakub Dawidek <nick@garage.freebsd.pl>

Add "GEOM_FOX", a class which detects and selects between multiple
redundant paths to the same device.

This class reacts to a label in the first sector of the device,
which is created the following way:

# "0123456789abcdef012345..."
# "<----magic-----><-id-...>
echo "GEOM::FOX someid" | dd of=/dev/da0 conv=sync

NB: Since the fact that multiple disk devices are in fact the same
device is not known to GEOM, the geom taste/spoil process cannot
fully catch all corner cases and this module can therefore be
confused if you do the right wrong things.

NB: The disk level drivers need to do the right thing for this to
be useful, and that is not by definition currently the case.