Fx.Morph faster styles processing

We can make the styles calculation faster, by removing prepending string from the list, coz it's always empty, something like

@@@javascript for (var i=0; i < after.length; i++) {
value = before[i] + (after[i] - before[i]) * delta; if (after.round) value = Math.round(value); after.t[i*2+1] = ''+value; } value = after.t.join('');
if (after.pre) value = after.pre + value;
style[key] = value;