UPDATE 1-India's Gail inks deal to buy U.S. LNG

* Cheniere to supply 3.5 mtpa of LNG to Gail over 20 years * Supply seen beginning in '17, pending regulatory approval * Cheniere expects another supply deal within weeks By Edward McAllister NEW YORK, Dec 12 (Reuters) - Cheniere Energy has signed a third long-term deal to export liquefied natural gas from its proposed plant in Louisiana, paving the way for the first U.S. export project of its kind in nearly 50 years. Cheniere will supply state-run Indian energy company Gail In