Markets ended mixed Friday with the S&P 500 ending the week just two points higher, but enough to give it a seventh straight week of gains. Some observers are starting to wonder if the rally that began at the beginning of the year on a deal to avoid the fiscal cliff is starting to run out of steam. The Dow has edged lower for two straight weeks. Walmart fell after Bloomberg News published excerpts from an internal e-mail that said February sales were a ‘‘total disaster.’’ The retailer said that sometimes internal communications ‘‘are not entirely accurate.’’ Energy companies also dipped as crude oil fell. Chevron dropped 75 cents.