More turnover in the upper ranks of an industry that has had a ton recently. Keith Rabois — one of the more prominent investors in Silicon Valley, and a close friend of Peter Thiel’s since they were a pair of controversial conservatives together as undergrads at Stanford — is teaming up again with his old friend. Rabois is joining Thiel’s venture capital firm, Founders Fund, as its newest general partner. It’s a major addition for the VC firm, which is a top performer but has seen a coincidentally high number of departures from its upper ranks in recent years.