Add shift+space functionality

js/reveal.js

@@ -1656,7 +1656,7 @@ var Reveal = (function(){
 
 		// Disregard the event if there's a focused element or a
 		// keyboard modifier key is present
-		if( hasFocus || event.shiftKey || event.altKey || event.ctrlKey || event.metaKey ) return;
+		if( hasFocus || (event.shiftKey && event.keyCode !== 32) || event.altKey || event.ctrlKey || event.metaKey ) return;
 
 		var triggered = true;
 
@@ -1683,7 +1683,7 @@ var Reveal = (function(){
 			// end
 			case 35: slide( Number.MAX_VALUE ); break;
 			// space
-			case 32: isOverview() ? deactivateOverview() : navigateNext(); break;
+			case 32: isOverview() ? deactivateOverview() : event.shiftKey ? navigatePrev() : navigateNext(); break;
 			// return
 			case 13: isOverview() ? deactivateOverview() : triggered = false; break;
 			// b, period, Logitech presenter tools "black screen" button