feature(script): improve cancel()

Allows passing an error object to `cancel(err)`, or an exception object returned by the deployd internal-client (eg. {message: "", status: 400}).

This allows easy chaining such as (in an event script):

```javascript
// call some other collection via internal-client
// both cases are handled by the new cancel, whether the code throws an Error object, or if .get returns an exception of the form {message, status}
dpd.somecol.get({...}).then(function() { error may get thrown here }.catch(cancel);
```

lib/internal-client.js

@@ -123,7 +123,11 @@ exports.build = function(server, session, stack, ctx) {
                 callback(data, null);
               }
             } else {
-              callback(null, data);
+              try {
+                callback(null, JSON.parse(data));
+              } catch (ex) {
+                callback(null, data);
+              }
             }
           },
           internal: true,

lib/script.js

@@ -1,7 +1,8 @@
 var _ = require('underscore')._
   , EventEmitter = require('events').EventEmitter
   , fs = require('fs')
-  , bluebird = require('bluebird');
+  , bluebird = require('bluebird')
+  , util = require('util');
 
 /**
  * A `Script` executes JavaScript src in a sandboxed context and exposes it a set of domain functions.
@@ -46,12 +47,22 @@ Script.prototype.run = function (ctx, domain, fn) {
     , session = ctx.session
     , waitingForCallback = false
     , callbackCount = 0
+    , isDone = false
     , events;
 
   var scriptContext = {
     'this': {},
     cancel: function(msg, status) {
-      var err = {message: msg, statusCode: status};
+      var err;
+      if (util.isError(msg)) {
+        err = msg;
+      } else if (!status && msg && msg.message && (msg.status || msg.statusCode)) {
+        // allow chaining this from another response
+        err = {message: msg.message, statusCode: msg.status || msg.statusCode};
+      } else {
+        err = {message: msg, statusCode: status};
+      }
+      done(err);
       throw err;
     },
     cancelIf: function(condition, msg, status) {
@@ -88,6 +99,8 @@ Script.prototype.run = function (ctx, domain, fn) {
   events = new EventEmitter();
 
   function done(err) {
+    if (isDone) return;
+    isDone = true;
     events.removeAllListeners('finishCallback');
     if (fn) fn(err);
   }

test/script.unit.js

@@ -16,6 +16,25 @@ describe('script', function(){
       });
     });
 
+    it('should keep error intact when calling cancel(err)', function(done) {
+      var s = new Script('cancel(new Error("test"))');
+      s.run({}, function (e) {
+        expect(e).to.exist;
+        expect(e.message).to.equal('test');
+        done();
+      });
+    });
+
+    it('should keep object intact when calling cancel({message: , status: })', function(done) {
+      var s = new Script('cancel({message: "test", status: 404})');
+      s.run({}, function (e) {
+        expect(e).to.exist;
+        expect(e.message).to.equal('test');
+        expect(e.statusCode).to.equal('404'); // status is turned into statusCode
+        done();
+      });
+    });
+
     it('should have access to the current user if one exists', function(done) {
       var s = new Script('if(!me) throw "no user"');
       var session = {