Enable the object-shorthand ESLint rule in src/shared

Please see http://eslint.org/docs/rules/object-shorthand.

For the most part, these changes are of the search-and-replace kind, and the previously enabled `no-undef` rule should complement the tests in helping ensure that no stupid errors crept into to the patch.

src/core/parser.js

@@ -1109,7 +1109,7 @@ var Linearization = {
                       'does not equal the stream length.');
     }
     return {
-      length: length,
+      length,
       hints: getHints(),
       objectNumberFirst: getInt('O'),
       endFirst: getInt('E'),