Make map and filter return type with a dispose method

Defined a KnockoutMappedObservableArray type which extends
KnockoutSubscription, providing a dispose() method since the mapped arrays
require disposal for proper cleanup.

knockout.projections/knockout.projections-tests.ts

@@ -54,3 +54,11 @@ var complexItems2 = sourceItems.map({
         };
     }
 });
+
+// Test disposal
+
+evenSquares.dispose();
+
+complexItems.dispose();
+
+complexItems2.dispose();

knockout.projections/knockout.projections.d.ts

@@ -5,18 +5,21 @@
 
 /// <reference path="../knockout/knockout.d.ts" />
 
+interface KnockoutMappedObservableArray<T> extends KnockoutObservableArray<T>, KnockoutSubscription {
+}
+
 interface KnockoutObservableArrayFunctions<T> {
     map<TResult>(mappingOptions: {
         mappingWithDisposeCallback: (value: T) => {
             mappedValue: TResult;
             dispose: () => void;
         };
-    }): KnockoutObservableArray<TResult>;
+    }): KnockoutMappedObservableArray<TResult>;
     map<TResult>(mappingOptions: {
         mapping: (value: T) => TResult;
         disposeItem?: (mappedItem: TResult) => void;
-    }): KnockoutObservableArray<TResult>;
-    map<TResult>(mappingOptions: (value: T) => TResult): KnockoutObservableArray<TResult>;
+    }): KnockoutMappedObservableArray<TResult>;
+    map<TResult>(mappingOptions: (value: T) => TResult): KnockoutMappedObservableArray<TResult>;
     
-    filter(predicate: (value: T) => boolean): KnockoutObservableArray<T>;
+    filter(predicate: (value: T) => boolean): KnockoutMappedObservableArray<T>;
 }