Slide effect: Handle string values for distance. Fixes #6637 - Slide …

…effect is jumpy with certain parameter combinations.

Thanks Jeff Roush.

ui/jquery.effects.slide.js

@@ -29,7 +29,7 @@ $.effects.slide = function(o) {
 		var ref = (direction == 'up' || direction == 'down') ? 'top' : 'left';
 		var motion = (direction == 'up' || direction == 'left') ? 'pos' : 'neg';
 		var distance = o.options.distance || (ref == 'top' ? el.outerHeight({margin:true}) : el.outerWidth({margin:true}));
-		if (mode == 'show') el.css(ref, motion == 'pos' ? -distance : distance); // Shift
+		if (mode == 'show') el.css(ref, motion == 'pos' ? (isNaN(distance) ? "-" + distance : -distance) : distance); // Shift
 
 		// Animation
 		var animation = {};