add dialect support checking to tests

this allows us to test for dialect features in tests, see
test/transaction.test.js for an example of checking for row locking
support before running a test

test/support.js

@@ -187,7 +187,8 @@ var Support = {
   }
 };
 
-var sequelize = Support.createSequelizeInstance();
+var sequelize = Support.sequelize = Support.createSequelizeInstance();
+
 //
 // For Postgres' HSTORE functionality and to properly execute it's commands we'll need this...
 before(function() {

test/transaction.test.js

@@ -4,8 +4,8 @@ var chai        = require('chai')
   , dialect     = Support.getTestDialect()
   , Promise     = require(__dirname + '/../lib/promise')
   , Transaction = require(__dirname + '/../lib/transaction')
-  , sinon       = require('sinon');
-
+  , sinon       = require('sinon')
+  , current     = Support.sequelize;
 
 describe(Support.getTestDialectTeaser("Transaction"), function () {
   this.timeout(4000);
@@ -55,7 +55,7 @@ describe(Support.getTestDialectTeaser("Transaction"), function () {
     });
   });
 
-  if (dialect !== 'sqlite') {
+  if (current.dialect.supports.lock) {
     describe('row locking', function () {
       this.timeout(10000);
       it('supports for update', function (done) {