Basically ripped over /tg/'s powernet and cable code into our own codebase.

Keeps Z-level code as it was.
Modifies/restores powernet procs as necessary to match our own implementation changes.

code/modules/shieldgen/sheldwallgen.dm

@@ -70,12 +70,12 @@
 	var/shieldload = between(500, max_stored_power - storedpower, power_draw)	//what we try to draw
 	shieldload = PN.draw_power(shieldload) //what we actually get
 	storedpower += shieldload
-	
+
 	//If we're still in the red, then there must not be enough available power to cover our load.
 	if(storedpower <= 0)
 		power = 0
 		return 0
-	
+
 	power = 1	// IVE GOT THE POWER!
 	return 1
 

code/modules/shieldgen/shield_capacitor.dm

@@ -107,14 +107,14 @@
 /obj/machinery/shield_capacitor/process()
 	if (!anchored)
 		active = 0
-	
+
 	//see if we can connect to a power net.
 	var/datum/powernet/PN
 	var/turf/T = src.loc
 	var/obj/structure/cable/C = T.get_cable_node()
 	if (C)
 		PN = C.powernet
-	
+
 	if (PN)
 		var/power_draw = between(0, max_charge - stored_charge, charge_rate) //what we are trying to draw
 		power_draw = PN.draw_power(power_draw) //what we actually get
@@ -138,7 +138,7 @@
 		active = !active
 	if( href_list["charge_rate"] )
 		charge_rate = between(10000, charge_rate + text2num(href_list["charge_rate"]), max_charge_rate)
-	
+
 	updateDialog()
 
 /obj/machinery/shield_capacitor/power_change()