获取设备的唯一标识uuid

摘自：http://blog.sina.com.cn/s/blog_5971cdd00102vqgy.html

-(NSString*) uuid {
CFUUIDRef puuid = CFUUIDCreate( nil );
CFStringRef uuidString = CFUUIDCreateString( nil, puuid );
NSString * result = (NSString *)CFStringCreateCopy( NULL, uuidString);
CFRelease(puuid);
CFRelease(uuidString); return [result autorelease];
}