Enhancement for netxml driver (by Vaclav Krpec)

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.