The Nitric Oxide-Donating Pravastatin Derivative, NCX 6550 [(1S-[1α(βS*, δS*), 2α, 6α, 8β-(R*), 8aα]]-1,2,6,7,8,8a-Hexahydro-β, δ, 6-trihydroxy-2-methyl-8-(2-methyl-1-oxobutoxy)-1-naphtalene-heptanoic Acid 4-(Nitrooxy)butyl Ester)], Reduces Splenocyte Adhesion and Reactive Oxygen Species Generation