fix several tutorial-related issues (jsdoc#222)

- Tutorial code allowed JSON files to have a .js extension, then tried
to parse all .js files as JSON. The code now only looks for JSON files
with a .json extension. This allows .js files and tutorials to live in
the same directory.
- Recent changes caused tutorials to be generated with the wrong
filename. This is now fixed.

rhino_modules/jsdoc/tutorial/resolver.js

@@ -14,7 +14,7 @@ var tutorial = require('jsdoc/tutorial'),
     hasOwnProp = Object.prototype.hasOwnProperty,
     conf = {},
     tutorials = {},
-    finder = /^(.*)\.(x(?:ht)?ml|html?|md|markdown|js(?:on)?)$/i;
+    finder = /^(.*)\.(x(?:ht)?ml|html?|md|markdown|json)$/i;
 
 /** Adds new tutorial.
     @param {tutorial.Tutorial} current - New tutorial.
@@ -75,7 +75,6 @@ exports.load = function(_path) {
                     break;
 
                 // configuration file
-                case 'js':
                 case 'json':
                     conf[name] = JSON.parse(content);
                     // don't add this as a tutorial
@@ -100,9 +99,7 @@ exports.resolve = function() {
         current;
     for (var name in conf) {
         if ( hasOwnProp.call(conf, name) ) {
-            // should we be restrictive here?
-            // what is someone just wants to keep sample sources in same directory with tutorials?
-            // I've decided to leave such cases alone
+            // TODO: should we complain about this?
             if (!(name in tutorials)) {
                 continue;
             }

rhino_modules/jsdoc/util/templateHelper.js

@@ -86,6 +86,11 @@ var linkMap = {
     urlToLongname: {}
 };
 
+var tutorialLinkMap = {
+    nameToUrl: {},
+    urlToName: {}
+};
+
 var longnameToUrl = exports.longnameToUrl = linkMap.longnameToUrl;
 
 var linkto = exports.linkto = function(longname, linktext) {
@@ -336,7 +341,15 @@ var tutorialToUrl = exports.tutorialToUrl = function(tutorial) {
         return;
     }
 
-    return 'tutorial-' + getUniqueFilename(node.name);
+    var url;
+    // define the URL if necessary
+    if (!tutorialLinkMap.nameToUrl[node.name]) {
+        url = 'tutorial-' + getUniqueFilename(node.name);
+        tutorialLinkMap.nameToUrl[node.name] = url;
+        tutorialLinkMap.urlToName[url] = node.name;
+    }
+
+    return tutorialLinkMap.nameToUrl[node.name];
 };
 
 /**