Make sure all CPUID values are handled, instead of exiting the
bhyve process when an unhandled one is encountered.

Hide some additional capabilities from the guest (e.g. debug store).

This fixes the issue with FreeBSD 9.1 MP guests exiting the VM on
AP spinup (where CPUID is used when sync'ing the TSCs) and the
issue with the Java build where CPUIDs are issued from a guest
userspace.

Submitted by:	tycho nightingale at pluribusnetworks com
Reviewed by:	neel
Reported by:	many
Allow 8259 registers to be read. This is a transient condition
during Linux boot.

Submitted by:	tycho nightingale at pluribusnetworks com
Reviewed by:	neel
Don't try to re-insert an already present but invalid page.

This could happen if a thread doing a page-in loses a ZFS range lock
race to a thread writing to the same range

This fixes "panic: vm_page_alloc: pindex already allocated" in
http://docs.FreeBSD.org/cgi/mid.cgi?1372165971.96049.42.camel

Submitted by:	avg
MFC after:	1 week
r251088 reverted the default value for UsePrivilegeSeparation from
"sandbox" to "yes", but did not update the documentation to match.