Stop ASIHTTPRequest subclasses from recreating statics on initialize and leaking in the process

Thanks to René Post for this fix!

@@ -45,13 +45,14 @@ static NSError *ASIUnableToCreateRequestError;
 
 + (void)initialize
 {
+	if (self == [ASIHTTPRequest class]) {
 		progressLock = [[NSRecursiveLock alloc] init];
-	
 		ASIRequestTimedOutError = [[NSError errorWithDomain:NetworkRequestErrorDomain code:ASIRequestTimedOutErrorType userInfo:[NSDictionary dictionaryWithObjectsAndKeys:@"The request timed out",NSLocalizedDescriptionKey,nil]] retain];	
 		ASIAuthenticationError = [[NSError errorWithDomain:NetworkRequestErrorDomain code:ASIAuthenticationErrorType userInfo:[NSDictionary dictionaryWithObjectsAndKeys:@"Authentication needed",NSLocalizedDescriptionKey,nil]] retain];
 		ASIRequestCancelledError = [[NSError errorWithDomain:NetworkRequestErrorDomain code:ASIRequestCancelledErrorType userInfo:[NSDictionary dictionaryWithObjectsAndKeys:@"The request was cancelled",NSLocalizedDescriptionKey,nil]] retain];
 		ASIUnableToCreateRequestError = [[NSError errorWithDomain:NetworkRequestErrorDomain code:ASIUnableToCreateRequestErrorType userInfo:[NSDictionary dictionaryWithObjectsAndKeys:@"Unable to create request (bad url?)",NSLocalizedDescriptionKey,nil]] retain];
-	
+	}
+	[super initialize];
 }
 
 - (id)initWithURL:(NSURL *)newURL