General Mills Inc GIS.N slipped on a deal to buy Tyson Foods Inc's TSN.N pet treats business for $1.2 billion in cash, as the cereal maker builds its pet food portfolio. By Medha Singh and Sruthi Shankar May 14 (Reuters) - Wall Street's main indexes were set to open higher at the end of a volatile week marred by worries about rising inflation and a subsequent tightening of monetary policy. Futures briefly pared gains after data showed U.S. retail sales unexpectedly stalled in April, as the boost from stimulus checks faded.