module: load JSON-LD with standard extension

The JSON-LD standard (http://www.w3.org/TR/json-ld/) requires sending
what is effectively JSON content using a different MIME type. Because
of that, it is usually required to use a file extension other than
.json since that is what is typically used in MIME type mapping in
HTTP servers. The IANA-registered file extension is .jsonld
(http://www.iana.org/assignments/media-types/application/ld+json).

This patch makes .jsonld documents loadable through require() in the
exact same manner that .json files are.

lib/module.js

@@ -444,6 +444,8 @@ Module._extensions['.json'] = function(module, filename) {
   }
 };
 
+// Native extension for .jsonld, same as JSON (but different MIME type)
+Module._extensions['.jsonld'] = Module._extensions['.json'];
 
 //Native extension for .node
 Module._extensions['.node'] = function(module, filename) {

test/fixtures/elementary.jsonld

@@ -0,0 +1,3 @@
+{
+  "@id":  "moo"
+}

test/fixtures/invalid.jsonld

@@ -0,0 +1,4 @@
+{
+  "@id":    "moo"
+  "@type":  "http://example.org"
+}

test/parallel/test-require-jsonld.js

@@ -0,0 +1,14 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+
+assert.throws(
+  function() {
+    require('../fixtures/invalid.jsonld');
+  },
+  /test[\/\\]fixtures[\/\\]invalid.jsonld: Unexpected string/,
+  'require() jsonld error should include path'
+);
+
+var ld = require('../fixtures/elementary.jsonld');
+assert.strictEqual(ld['@id'], 'moo', 'require() loads jsonld');