Do not cache modules that throw exceptions

If a module throws an exception on load, it should not be cached.
This patch shows the problem in a test case and also fixes it.

See: https://groups.google.com/forum/#!topic/nodejs-dev/1cIrvJcADbY

Closes GH-707
Closes GH-710

lib/module.js

@@ -270,7 +270,13 @@ Module._load = function(request, parent, isMain) {
   }
 
   Module._cache[filename] = module;
+  try {
     module.load(filename);
+  } catch (err) {
+    delete Module._cache[filename];
+    throw err;
+  }
+
   return module.exports;
 };
 

test/simple/test-require-exceptions.js

@@ -0,0 +1,12 @@
+var common = require('../common');
+var assert = require('assert');
+
+// A module with an error in it should throw
+assert.throws(function() {
+  require(common.fixturesDir + '/throws_error');
+});
+
+// Requiring the same module again should throw as well
+assert.throws(function() {
+  require(common.fixturesDir + '/throws_error');
+});