Make wrench usable independently of technic

wrench/depends.txt

@@ -1,6 +1,6 @@
 default
-technic
-technic_chests
-technic_worldgen
+technic?
+technic_chests?
+technic_worldgen?
 intllib?
 

wrench/support.lua

@@ -66,6 +66,8 @@ function wrench:original_name(name)
 end
 
 function wrench:register_node(name, def)
+	if minetest.registered_nodes[name] then
 	    self.registered_nodes[name] = def
 	end
+end
 

wrench/technic.lua

@@ -323,6 +323,7 @@ for i = 1, 15 do
 	})
 end
 
+if minetest.get_modpath("technic") then
     for tier, _ in pairs(technic.machines) do
 		local ltier = tier:lower()
 		for i = 0, 8 do
@@ -338,4 +339,5 @@ for tier, _ in pairs(technic.machines) do
 			})
 		end
 	end
+end