debug - Add -v option to vmobjinfo and memory/swap dump

* If the -v option is used, the contents of the memory AND swap space
  associated with the VM object to be dumped.

* Allow swap devices to be specified on the command line.  If not specified,
  only active memory is dumped with -v.

* Fixups for new VM object hash table in the kernel.
u4b - implement usb_filter_write(), fix issues w/apcupsd

* Implement usb_filter_write() (poll, kqueue).

* This fixes a live loop in apcupsd when it is configured
  to talk to the UPS over a usb port.
Check __BSD_VISIBLE's actual value, not just if it is defined.

It could be defined to 0, per <sys/cdefs.h>. Only the few cases which
this commit fixes were wrong.