HOUSTON, May 23 (Reuters) - Republican presidential candidate Donald Trump raised tens of millions of dollars during a fundraising swing through Texas this week, promising he would support the oil and gas industry by backing new pipelines and restoring fracking on federal land. [cut] A Houston fundraiser on Wednesday was hosted by oil billionaires Jeff Hildebrand, founder of Hilcorp Energy, the largest closely held U.S. oil firm; George Bishop, founder of GeoSouthern Energy; Harold Hamm, founder of Continental Resources; and Kelcy Warren, head of pipeline firm Energy Transfer Partners. Trump drew standing ovations when he promised to get more natural...