Added new entity info_custommessage

Allows map editors to concatenate a sequence of strings and then
displays it using one of the pre-existing messaging entities, useful for
A = B/C messages.

Keys:
displayentity(targetname) : The entity used to display the message, can
be a targetname of a class game_text, point_worldhint or point_zsmessage
zsmessagemode(choices) : If using a point_zsmessage, select the method
of display with this key
"0"  : "Centred HUD Message"
"1"  : "Corner Human HUD Message"
"2"  : "Corner Zombie HUD Message"
string01(string) : Part 01 of the full string
string##(string) : Part ## of the full string, there can be up to 99 of
these.

Inputs:
displaystrings(string): Concatenates and displays the full string using
the attached entity
setstring##(string) : Sets part ## of the full string, there can be up
to 99 of these.

Outputs:
OnDisplayed : Called when the message has successfully displayed.

gamemodes/zombiesurvival/entities/entities/info_custommessage/init.lua

@@ -0,0 +1,69 @@
+ENT.Type = "point"
+
+function ENT:Initialize()
+	if not self.Initialized then -- Why is KeyValue() called before Initialize()?
+		self.PartStrings = {} 
+		self.Initialized = true
+		self.DisplayTarget = self.DisplayTarget or ""
+		self.ZSMessageMode = self.ZSMessageMode or 0
+	end 
+end
+
+function ENT:Think()
+end
+
+function ENT:DisplayStrings()
+	local FullString = ""
+	for k,v in pairs(self.PartStrings) do
+		FullString = FullString .. v
+	end
+	for k,v in pairs(ents.FindByName(self.DisplayTarget)) do
+		local EntityClass = v:GetClass()
+		if EntityClass == "game_text" then
+			v:Input("AddOutput", self, self, "message "..FullString)
+			v:Input("Display", self, self, FullString)
+		elseif EntityClass == "point_zsmessage" then
+			if self.ZSMessageMode == "1" then
+				v:Input("sethumanhudmessage", self, self, FullString)
+			elseif self.ZSMessageMode == "2" then
+				v:Input("setzombiehudmessage", self, self, FullString)
+			else
+				v:Input("message", self, self, FullString)
+			end
+		elseif EntityClass == "point_worldhint" then
+			v:Input("sethint", self, self, FullString)
+		end
+	end
+	self:Input("OnDisplayed", self, self, FullString)
+end
+
+function ENT:AcceptInput(name, activator, caller, args)
+	name = string.lower(name)
+	if string.sub(name, 1, 2) == "on" then
+		self:FireOutput(name, activator, caller, args)
+	elseif string.sub(name, 1, 9) == "setstring" then
+		self:KeyValue(string.sub(name, 4,11),args)
+	elseif name == "displaystrings" then
+		self:DisplayStrings()
+	end
+end
+
+function ENT:KeyValue(key, value)
+	key = string.lower(key)
+	if string.sub(key, 1, 6) == "string" then 
+		if not self.Initialized then 
+			self.PartStrings = {} 
+			self.Initialized = true
+		end 
+		local part = tonumber(string.sub(key,7,8))
+		if part ~= nil then 
+			self.PartStrings[part] = value
+		end
+	elseif key == "displayentity" then
+		self.DisplayTarget = value
+	elseif key == "zsmessagemode" then
+		self.ZSMessageMode = value
+	elseif string.sub(key, 1, 2) == "on" then
+		self:AddOnOutput(key, value)
+	end
+end