Introduce FirstOrDefault extensions method for Array.Find and List.Find.

This allows the LINQ spelling to be used, but benefits from the performance improvement of the specific methods for these classes that provide the same result.

OpenRA.Mods.Common/Scripting/Global/PlayerGlobal.cs

@@ -9,7 +9,6 @@
  */
 #endregion
 
-using System;
 using System.Linq;
 using Eluant;
 using OpenRA.Scripting;
@@ -25,7 +24,7 @@ namespace OpenRA.Mods.Common.Scripting
 		[Desc("Returns the player with the specified internal name, or nil if a match is not found.")]
 		public Player GetPlayer(string name)
 		{
-			return Array.Find(Context.World.Players, p => p.InternalName == name);
+			return Context.World.Players.FirstOrDefault(p => p.InternalName == name);
 		}
 
 		[Desc("Returns a table of players filtered by the specified function.")]