By Yeganeh Torbati DUBAI (Reuters) - Iranians are struggling with slower Internet speeds and limited access ahead of an unpredictable presidential election that has put hardline Islamist authorities on alert for possible unrest. Experts and web users say they believe the Internet obstacles are related to the June 14 presidential vote, the first since 2009 polls in which accusations of fraud - denied by the government - kindled months of protests organised in part via social networking sites like Facebook and Twitter. ...