Fix Low Battery detection with ConnectUPS cards

The low battery OID itself cannot be read directly.
Low battery alarms OID appears in an alarm array.
Fix wrong OFF status reported when on battery.

UPS.BatterySystem.Charger.PresentStatus.Used is not related to UPS outputs being on or off but rather to the charger being on or off.
Define _REENTRANT for all Solaris and AIX platforms.

This is essentially the final commit in pull request #39.
Fix AIX linkage of do_upsconf_args()

Closes #58 (GitHub pull request "Fix AIX build")

(cherry picked from commit 5fc7518f97d2738d791c3c77f2257d05e3a9da3b)
netxml: added RW access, fixed FSD/shutdown duration bugs, etc.

 * Fixed bugs in resolution of FSD condition and computation of shutdown
duration.
 * Added System.* UPS variables.
 * Enabled RW access to appropriate UPS variables.
 * Added UPS veriables value convertors.
 * Added support for XML protocol v3 {GET|SET}_OBJECT query implementing getvar
and setvar routines.
 * netxml driver man page updated to include info about the driver-specific
configuration parameters.

Closes #59 (GitHub pull request: "Enhancement for netxml driver")

Pull request by: Frédéric BOHE <fredericbohe@eaton.com>
Merge remote-tracking branch 'fbohe/fix_connectups_lb_detection'

Fixes the LB detection on the powerware MIB handler for snmp-ups.
Merge remote-tracking branch 'fbohe/fix_wrong_OFF_status'

For mge-hid subdriver of usbhid-ups.
Nutscan fix and enhancement

Closes #60 (GitHub Pull Request via fbohe)
[nut-scanner] Remove unused variable