Hill: Washington, D.C.'s NBC television station refused to broadcast Keystone XL pipeline foe Tom Steyers ad attacking the project during President Obamas Tuesday appearance on "The Tonight Show." On Tuesday E2-Wire wrote about the ad and oil industry criticism of it here. A spokesman for NBC-owned WRC-TV said Wednesday morning that after a careful review, it was determined that this ad violates our guidelines. We have communicated that to the advertiser. The billionaire climate activist Steyer,...