* Second assassination of secular politician this year
* Anti-Islamist protests erupt in Tunis, Sidi Bouzid
* Main Islamist Ennahda party condemns killing
* Brahmi's family accuses Ennahda of responsibility (Adds details, quotes, background, call for strike)
By Tarek Amara
TUNIS, July 25 (Reuters) - Tunisian opposition politicianMohamed Brahmi was shot dead outside his home in ...