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

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

Fix an off-by-one error in the range check for the maximal -i or -o
block size.

Fix my own style(9) bugs:

. forward declare all static functions
. add a couple of redundant parens in return statements where they've
been missing
. remove the space after exit since it's a function

This commit was generated by cvs2svn to compensate for changes in r129330,
which included commits to RCS files with non-trunk default branches.

This is smbmsg(8), a small utility to send/receive SMBus messages.

Also included is a `bus-probe' modus of operation to help scanning
an I2C bus.