Bump FreeBSD_version due to changed header for strcasecmp(3) family.

In r266865, strcasecmp_l() and strncasecmp_l() were moved from
<string.h> to <strings.h> for POSIX 2008 compliance.

Requested by:	linimon
Remove bogus check for kmem_malloc() failure even though M_WAITOK is set.

Requested by:	jkim
Rework the notion of CPU used in top.  In particular, for subsequent
displays after a pause, use the difference in runtime divided by the
length of the pause as the percentage of CPU used instead of the value
calculated by the kernel.  In addition, when determing if a process or
thread is idle or not, treat any process or thread that has used any
runtime or performed any context switches during the interval as busy.

Note that the percent CPU is calculated as a double and stored in an
array to avoid recalculating the value multiple times in the comparison
method used to sort processes in the CPU display.

Tested by:	Jamie Landeg-Jones <jamie@dyslexicfish.net>
Reviewed by:	emaste (earlier version)
MFC after:	1 week