Refactor download mechanism to allow multiple concurrent downloads. Allow downloads to be cancelled. Allow js to query if files exist in the cache. Fix some compiler warnings.

OpenRA.Launcher.Mac/Download.h

@@ -0,0 +1,23 @@
+//
+//  Download.h
+//  OpenRA
+//
+//  Created by Paul Chote on 19/11/10.
+//  Copyright 2010 __MyCompanyName__. All rights reserved.
+//
+
+#import <Cocoa/Cocoa.h>
+@class GameInstall;
+@interface Download : NSObject
+{
+	NSString *key;
+	NSString *url;
+	NSString *filename;
+	GameInstall *game;
+	NSTask *task;
+}
++ (id)downloadWithURL:(NSString *)aURL filename:(NSString *)aFilename key:(NSString *)aKey game:(GameInstall *)aGame;
+- (id)initWithURL:(NSString *)aURL filename:(NSString *)aFilename key:(NSString *)aKey game:(GameInstall *)game;
+- (void)cancel;
+
+@end