add dialect checks for upsert support

Upserts in MSSQL are non-trivial to implement, adding the ability
to test for support is a valid stopgap for later implementation

lib/dialects/abstract/index.js

@@ -34,6 +34,7 @@ AbstractDialect.prototype.supports = {
   schemas: false,
   transactions: true,
   migrations: true,
+  upserts: true,
   constraints: {
     restrict: true
   },

test/dao-factory/update.test.js

@@ -12,7 +12,8 @@ var chai      = require('chai')
   , dialect   = Support.getTestDialect()
   , datetime  = require('chai-datetime')
   , _         = require('lodash')
-  , assert    = require('assert');
+  , assert    = require('assert')
+  , current   = Support.sequelize;
 
 chai.use(datetime);
 chai.config.includeStack = true;
@@ -40,6 +41,7 @@ describe(Support.getTestDialectTeaser("DAOFactory"), function () {
     this.clock.restore();
   });
 
+  if (current.dialect.supports.upserts) {
     describe('upsert', function () {
       it('works with upsert on id', function () {
         return this.User.upsert({ id: 42, username: 'john' }).bind(this).then(function (created) {
@@ -91,4 +93,6 @@ describe(Support.getTestDialectTeaser("DAOFactory"), function () {
         });
       });
     });
+  }
+
 });