CLJS-3147: Allow Node require from foreign lib

Export require to global.

Author: swannodette

src/main/cljs/cljs/bootstrap_nodejs.js

@@ -108,12 +108,26 @@ global.CLOSURE_LOAD_FILE_SYNC = function(src) {
 
 // Declared here so it can be used to require base.js
 function nodeGlobalRequire(file) {
-    var _module = global.module, _exports = global.exports;
+    var _module  = global.module,
+        _exports = global.exports,
+        exportedRequire = false;
+
     global.module = undefined;
     global.exports = undefined;
+
+    if(global.require == undefined) {
+        exportedRequire = true;
+        global.require = require;
+    }
+
     vm.runInThisContext.call(global, fs.readFileSync(file), file);
+
     global.exports = _exports;
     global.module = _module;
+
+    if(exportedRequire) {
+        global.require = undefined;
+    }
 }