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

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

Decode as many or as few partition entries as the label claims there
are. We have already checked it against the caller provided maxpart.

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

Use __FBSDID().

Approved by: phk

Remove debugging printfs which should not have been committed.

Make bsd_disklabel_le_enc calculate the checksum and fill it in.
(If there is a legitimate need to correctly encode and pack a
disklabel with an invalid checksum custom tools can be built for
that.)

Make bsd_disklabel_le_dec() validate the magics, number of partitions
(against a new parameter) and the checksum.

Vastly simplify the logic of the GEOM::BSD class implementation:

Let g_bsd_modify() always take a byte-stream label.

This simplifies all users, except the ioctl's which now have to
convert to a byte-stream first. Their loss.

g_bsd_modify() is called with topology held now, and it returns
with it held.

Always update the md5sum in g_bsd_modify(), otherwise the check
is no use after the first modification of the label. Make the
MD5 over the bytestream version of the label.

Move the rawoffset hack to g_bsd_modify() and remove all the
inram/ondisk conversions.

Don't configure hotspots in g_bsd_modify(), do it in taste instead,
we do not support moving the label to a different location on the
fly anyway.

This passes all current regression tests.

Pull in bcopy() prototype from <string.h> when compiled in userland.

These two files fell off during my previous commit: put the encoding
decoding functions for struct disklabel in a separate .c file.