Fix link dragging to text editors

We were just adding double square brackets if the title contains
spaces. We should be adding them if the title is not a valid wikilink.

core/modules/widgets/link.js

@@ -155,7 +155,7 @@ LinkWidget.prototype.handleDragStartEvent = function(event) {
 			dataTransfer.clearData();
 			var jsonData = this.wiki.getTiddlerAsJson(this.to),
 				textData = this.wiki.getTiddlerText(this.to,""),
-				title = this.to.indexOf(" ") === -1 ? this.to : "[[" + this.to + "]]";
+				title = (new RegExp("^" + $tw.config.textPrimitives.wikiLink + "$","mg")).exec(this.to) ? this.to : "[[" + this.to + "]]";
 			// IE doesn't like these content types
 			if(!$tw.browser.isIE) {
 				dataTransfer.setData("text/vnd.tiddler",jsonData);