tripplite_usb: use dv/dq charge calculation for all models (0.21)
HCL: GRAFENTHAL PR-3000-HS supported by snmp-ups

Tested with 2.6.5-3 (0.68) on Windows (IETF MIB 1.4).

Some NUT variables are zero - further testing may be needed.

Reference: http://news.gmane.org/find-root.php?message_id=75FC7A5479BA4A4E8ADF76BC3AD3E568581EC753%40MS03.MACLE.DE
tripplite_usb: expose battery_min/_max as variables (0.22)

http://news.gmane.org/find-root.php?message_id=21370.36829.817425.464627%40godel.bruda.ca
Merge branch 'tl_charge_3003': tripplite_usb battery.charge config
tripplite_usb: silence warning (0.23)

Pedantic, to be sure, but someone might try the driver with a protocol not
listed, and sure enough, bv_12V won't be initialized.
tripplite_usb: last tweaks, for now.

Initialize bv_12V to a dummy value, since gcc can't see that it is used in the
union of both conditionals where it is set.

Also, align the documentation with the strange definition of empty used by the
Tripp Lite state-of-charge approximation.