Fix memleak in vm.runInNewContext

Closes GH-704.

src/node_script.cc

@@ -355,7 +355,14 @@ Handle<Value> WrappedScript::EvalMachine(const Arguments& args) {
 
   if (output_flag == returnResult) {
     result = script->Run();
-    if (result.IsEmpty()) return try_catch.ReThrow();
+    if (result.IsEmpty()) {
+      if (context_flag == newContext) {
+        context->DetachGlobal();
+        context->Exit();
+        context.Dispose();
+      }
+      return try_catch.ReThrow();
+    }
   } else {
     WrappedScript *n_script = ObjectWrap::Unwrap<WrappedScript>(args.Holder());
     if (!n_script) {

test/pummel/test-vm-memleak.js

@@ -0,0 +1,27 @@
+var assert = require('assert');
+var common = require('../common');
+
+var start = Date.now();
+var maxMem = 0;
+
+var interval = setInterval(function() {
+  try {
+    require('vm').runInNewContext('throw 1;');
+  } catch(e) {
+  }
+
+  var rss = process.memoryUsage().rss;
+  maxMem = Math.max(rss, maxMem);
+
+
+  if (Date.now() - start > 5*1000) {
+    // wait 10 seconds.
+    clearInterval(interval);
+  }
+}, 1);
+
+process.on('exit', function() {
+  console.error('max mem: %dmb', Math.round(maxMem / (1024*1024)));
+  // make sure we stay below 100mb
+  assert.ok(maxMem < 50 * 1024 * 1024);
+});