set the _dialect on query generator in dialect specific tests

lib/sequelize.js

@@ -113,7 +113,7 @@ module.exports = (function() {
     }
 
     try {
-      this.dialect            = new (require("./dialects/" + this.getDialect()))(this)
+      this.dialect          = new (require("./dialects/" + this.getDialect()))(this)
     } catch(err) {
       throw new Error("The dialect " + this.getDialect() + " is not supported.")
     }

test/mysql/query-generator.test.js

@@ -516,6 +516,7 @@ if (Support.dialectIsMySQL()) {
               test.arguments[1] = test.arguments[1](this.sequelize)
             }
             QueryGenerator.options = context.options
+            QueryGenerator._dialect = this.sequelize.dialect
             var conditions = QueryGenerator[suiteTitle].apply(QueryGenerator, test.arguments)
             expect(conditions).to.deep.equal(test.expectation)
             done()

test/postgres/query-generator.test.js

@@ -904,6 +904,7 @@ if (dialect.match(/^postgres/)) {
               test.arguments[1] = test.arguments[1](this.sequelize)
             }
             QueryGenerator.options = context.options
+            QueryGenerator._dialect = this.sequelize.dialect
             var conditions = QueryGenerator[suiteTitle].apply(QueryGenerator, test.arguments)
             expect(conditions).to.deep.equal(test.expectation)
             done()

test/sqlite/query-generator.test.js

@@ -444,6 +444,7 @@ if (dialect === 'sqlite') {
               test.arguments[1] = test.arguments[1](this.sequelize)
             }
             QueryGenerator.options = context.options
+            QueryGenerator._dialect = this.sequelize.dialect
             var conditions = QueryGenerator[suiteTitle].apply(QueryGenerator, test.arguments)
             expect(conditions).to.deep.equal(test.expectation)
             done()