[runmode addon] Include CodeMirror.innerMode in runmode.node.js

The markdown mode uses `CodeMirror.innerMode` which isn't defined in
the stripped down node runmode. Since markdown is the only mode
(AFAICT) that uses it I'm not sure if it would make more sense rewrite
it to not use it but this seemed like the least risky option.

Author: niik

addon/runmode/runmode.node.js

@@ -163,6 +163,18 @@ exports.getMode = function(options, spec) {
 
   return modeObj;
 };
+
+exports.innerMode = function(mode, state) {
+  var info;
+  while (mode.innerMode) {
+    info = mode.innerMode(state);
+    if (!info || info.mode == mode) break;
+    state = info.state;
+    mode = info.mode;
+  }
+  return info || {mode: mode, state: state};
+}
+
 exports.registerHelper = exports.registerGlobalHelper = Math.min;
 
 exports.runMode = function(string, modespec, callback, options) {