Fix #169. Expose require members in the repl.

This fixes #169 by putting the require members onto the cwdRequire function
which is exposed to the repl scope.

lib/repl.js

@@ -24,6 +24,9 @@ function cwdRequire (id) {
   }
   return require(id);
 }
+Object.keys(require).forEach(function (k) {
+  cwdRequire[k] = require[k];
+});
 
 function setScope (self) {
   scope = {};