Relax external link matching to ignore illegal characters

Fixes #2501, and rolls back some of #2324

core/modules/utils/utils.js

@@ -495,7 +495,7 @@ exports.escapeRegExp = function(s) {
 
 // Checks whether a link target is external, i.e. not a tiddler title
 exports.isLinkExternal = function(to) {
-	var externalRegExp = /^(?:file|http|https|mailto|ftp|irc|news|data|skype):[^\s<>{}\[\]`|"\\^]+(?:\/|\b)$/i;
+	var externalRegExp = /^(?:file|http|https|mailto|ftp|irc|news|data|skype):[^\s<>{}\[\]`|"\\^]+(?:\/|\b)/i;
 	return externalRegExp.test(to);
 };