Check if the specified group is the user's primary group before
iterating over the (possibly empty) list of members.  Otherwise, we
get a false negative when the target group has no members listed in
/etc/group.  This went mostly unnoticed because root is explicitly
listed as a member of wheel, so the bug is never triggered in the most
common use case, which is su(8).

PR:		109416
MFC after:	1 week
Handle nested exceptions in bhyve.

A nested exception condition arises when a second exception is triggered while
delivering the first exception. Most nested exceptions can be handled serially
but some are converted into a double fault. If an exception is generated during
delivery of a double fault then the virtual machine shuts down as a result of
a triple fault.

vm_exit_intinfo() is used to record that a VM-exit happened while an event was
being delivered through the IDT. If an exception is triggered while handling
the VM-exit it will be treated like a nested exception.

vm_entry_intinfo() is used by processor-specific code to get the event to be
injected into the guest on the next VM-entry. This function is responsible for
deciding the disposition of nested exceptions.
Add support for the "account" facility.

PR:		115164
MFC after:	1 week