Ports more of /tg/'s powernet code.

Among other things this fixes a a bug where SMES would draw excess power from the powergrid they were outputting to, rather than drawing from.

code/game/area/Space Station 13 areas.dm

@@ -33,7 +33,6 @@ NOTE: there are two lists of areas in the end of this file: centcom and station
 	var/eject = null
 
 	var/debug = 0
-	var/powerupdate = 10		//We give everything 10 ticks to settle out it's power usage.
 	var/requires_power = 1
 	var/unlimited_power = 0
 	var/always_unpowered = 0	//this gets overriden to 1 for space in area/New()