Bump max rule size to 512 opcodes.
Add movw and movt relocations to the list of relocations against function
names that must nnot be adjusted. This fixes a bug where code such as:
movw r2, :lower16:symbol
movt r2, :upper16:symbol

It is common for clang to generate such code when targeting armv7.
Put and #ifdef _KERNEL around the #include for opt_capsicum.h to
hopefully allow the build to finish after r272505.
Silence a warning about Tag_Virtualization_use being unknown. We don't
handle merging this tag correctly, however it's unused.
Don't make nested definition for range_seg_cache.

Reported by:	ian
MFC after:	1 week
X-MFC-With:	r272506
Make kevent(2) periodic timer events more reliably periodic.  The event
callout is now scheduled using the C_ABSOLUTE flag, and the absolute time
of each event is calculated as the time the previous event was scheduled
for plus the interval.  This ensures that latency in processing a given
event doesn't perturb the arrival time of any subsequent events.

Reviewed by:	jhb