Replace CAP_POLL_EVENT and CAP_POST_EVENT capability rights (which I had
a very hard time to fully understand) with much more intuitive rights:

	CAP_EVENT - when set on descriptor, the descriptor can be monitored
		with syscalls like select(2), poll(2), kevent(2).

	CAP_KQUEUE_EVENT - When set on a kqueue descriptor, the kevent(2)
		syscall can be called on this kqueue to with the eventlist
		argument set to non-NULL value; in other words the given
		kqueue descriptor can be used to monitor other descriptors.
	CAP_KQUEUE_CHANGE - When set on a kqueue descriptor, the kevent(2)
		syscall can be called on this kqueue to with the changelist
		argument set to non-NULL value; in other words it allows to
		modify events monitored with the given kqueue descriptor.

Add alias CAP_KQUEUE, which allows for both CAP_KQUEUE_EVENT and
CAP_KQUEUE_CHANGE.

Add backward compatibility define CAP_POLL_EVENT which is equal to CAP_EVENT.

Sponsored by:	The FreeBSD Foundation
MFC after:	3 days
Correct right names.

Sponsored by:	The FreeBSD Foundation
MFC after:	3 days
Fix a couple of issues with -F:
- Fix ALWAYS_INSTALL to take precedence over the FreeBSD ID checks.
  In particular, always install a file where the only change was
  the FreeBSD ID even if -F is specified.
- Fix the -F option in the case that the only upstream change is a
  change in the FreeBSD ID and the local file is removed.
- Add tests for these two cases.