Initial MSSQL related commit.
Merge branch 'master' of github.com:yiisoft/yii2 into mssql

Conflicts:
	yii/db/Connection.php
MSSQL driver classes moved to the proper location.
RBAC: Item and Assignment optimized save approach
MSSQL table metadata parsint (initial version).
MSSQL Schema: methods order changed, initial data type infer.
Initial MSSQL tests.
Merge branch 'master' of github.com:yiisoft/yii2 into mssql
"YiiRequirementChecker" has been created as blank.
Method "YiiRequirementChecker::check()" has been implemented.
Method "YiiRequirementChecker::check()" has been refactored to be used in method chain.
Methods "YiiRequirementChecker::getResults()" and "YiiRequirementChecker::render()" have been added.
Test case "YiiRequirementCheckerTest::testCheckEval()" has been added.
better testing: time()-function-mock

as discussed in #203
https://github.com/yiisoft/yii2/issues/203#issuecomment-17759631
"YiiRequirementChecker::check()" has been updated to be able to collect different requirements set in the chained call.
mocking time in test only usefull when using time() once

https://github.com/yiisoft/yii2/commit/e2513de6c6207fa37894a944e10b8cd420ac6804#commitcomment-3192244
added newline to end of header and body blocks in View

issue #237
"YiiRequirementChecker::render()" has been implemented, console view has been created.
Web view for "YiiRequirementChecker" has been created.
Check helper methods have been added to "YiiRequirementChecker".
"YiiRequirementChecker::check()" has been updated allowing to accept filename for the requirements.
Yii core requirements file has been composed.