Make sure truncate: true is still allowed in Model.destroy() and add a test for it

lib/model.js

@@ -1415,8 +1415,8 @@ module.exports = (function() {
     var self = this
       , instances;
 
-    if (!options || !options.where) {
-      throw new Error('Missing where attribute in the options parameter passed to destroy.');
+    if (!options || !(options.where || options.truncate)) {
+      throw new Error('Missing where or truncate attribute in the options parameter passed to destroy.');
     }
 
     options = Utils._.extend({

test/model.test.js

@@ -1094,6 +1094,22 @@ describe(Support.getTestDialectTeaser('Model'), function() {
   });
 
   describe('destroy', function() {
+    it('truncate should clear the table', function() {
+      var User = this.sequelize.define('User', { username: DataTypes.STRING }),
+          data = [
+            { username: 'user1' },
+            { username: 'user2' }
+          ];
+
+      return this.sequelize.sync({ force: true }).then(function() {
+        return User.bulkCreate(data);
+      }).then(function() {
+        return User.destroy({ truncate: true });
+      }).then(function() {
+        return expect(User.findAll()).to.eventually.have.length(0);
+      });
+    });
+
     it('throws an error if no where clause is given', function() {
       var User = this.sequelize.define('User', { username: DataTypes.STRING });
 
@@ -1102,7 +1118,8 @@ describe(Support.getTestDialectTeaser('Model'), function() {
       }).then(function() {
         throw new Error('Destroy should throw an error if no where clause is given.');
       }, function(err) {
-        expect(err.message).to.equal('Missing where attribute in the options parameter passed to destroy.');
+        expect(err).to.be.an.instanceof(Error);
+        expect(err.message).to.equal('Missing where or truncate attribute in the options parameter passed to destroy.');
       });
     });