Fix leak and change comment to reflect new behaviour

@@ -192,7 +192,7 @@ typedef void (^ASIDataBlock)(NSData *data);
 	NSString *username;
 	NSString *password;
 	
-	// Global User-Agent for requests unless one is provided for a specific request
+	// User-Agent for this request
 	NSString *userAgent;
 	
 	// Domain used for NTLM authentication

@@ -389,6 +389,7 @@ static NSOperationQueue *sharedQueue = nil;
 	[connectionInfo release];
 	[requestID release];
 	[dataDecompressor release];
+	[userAgent release];
 
 	#if NS_BLOCKS_AVAILABLE
 	[self releaseBlocksOnMainThread];