Mast Cell Stabilizer Ketotifen [4-(1-Methyl-4-piperidylidene)-4H-benzo[4,5]cyclohepta[1,2-b]thiophen-10(9H)-one Fumarate] Prevents Mucosal Mast Cell Hyperplasia and Intestinal Dysmotility in Experimental Trichinella spiralis Inflammation in the Rat