Added a clock_seconds() function prototype to core/sys/clock.h, that returns seconds in 32 bit format.
Added a clock_seconds() function prototype to core/sys/clock.h, that returns seconds in 32 bit format.

bluerover/6lbr,bluerover/6lbr,bluerover/6lbr,MohamedSeliem/contiki,bluerover/6lbr,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,bluerover/6lbr,arurke/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki,bluerover/6lbr,MohamedSeliem/contiki,bluerover/6lbr,MohamedSeliem/contiki,arurke/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki