Implement IEquatable on structs.

Any struct which overrides object.Equals(object obj) should implement IEquatable<T> to gain a more efficient Equals(T other) overload. This overload will be used by hashing collections like Dictionary which enables them to check equality without boxing the struct.

OpenRA.Game/Primitives/Rectangle.cs

@@ -13,7 +13,7 @@ using System;
 
 namespace OpenRA.Primitives
 {
-	public struct Rectangle
+	public struct Rectangle : IEquatable<Rectangle>
 	{
 		// TODO: Make these readonly: this will require a lot of changes to the UI logic
 		public int X;
@@ -76,6 +76,11 @@ namespace OpenRA.Primitives
 			return Contains(pt.X, pt.Y);
 		}
 
+		public bool Equals(Rectangle other)
+		{
+			return this == other;
+		}
+
 		public override bool Equals(object obj)
 		{
 			if (!(obj is Rectangle))