SAN FRANCISCO (Reuters) - Facebook's original friends are moving into politics. Small investments in NationBuilder, a political campaign software startup, by a tight-knit group of Facebook alumni suggest how they might spread their wealth around Silicon Valley in coming months, especially after the world's largest Internet social network goes public. NationBuilder said Thursday it has raised $6.25 million in an investment round led by Andreessen Horowitz, the venture capital firm founded by high-tech entrepreneurs Marc Andreessen and Ben Horowitz. ...