WASHINGTON (Reuters) - The Obama administration unveiled long-awaited rules on Friday to bolster oversight of so-called "fracking" on public lands, seeking to allay concerns over the technology that has spurred a U.S. boom in shale gas drilling. The Interior Department proposal would require that companies obtain government approval to use hydraulic fracturing, or fracking, in drilling for natural gas on federal lands. The rules would not affect drilling on private land, where the bulk of shale exploration is taking place. ...