Update DatabaseDriverTest.php

SQL Server does not support unsigned integers
Improved error messages in Paginator: LimitSubqueryOutputWalker

The already existing follow-up check throwing "Not all identifier properties can be found in the ResultSetMapping: %s" is a much more technical description.

If $sqlIdentifier is empty (count 0) it can be concluded that there are no mapped results. An alternative error message could thus be "The Paginator does not support queries without mapped results." (line 153).

Possibly '!=' on line 154 could be replaced by '>' because i think this is the only situation that can occur. But since i don't know this for sure, i left it like i found it.
Improved error messages in Paginator: LimitSubqueryOutputWalker



The already existing follow-up check throwing "Not all identifier properties can be found in the ResultSetMapping: %s" is a much more technical description.

If $sqlIdentifier is empty (count 0) it can be concluded that there are no mapped results. An alternative error message could thus be "The Paginator does not support queries without mapped results." (line 153).

Possibly '!=' on line 154 could be replaced by '>' because i think this is the only situation that can occur. But since i don't know this for sure, i left it like i found it.

Didn't use elseif in this commit as per Stof his suggestion.
Update SqlWalker.php fixed wrong GROUP BY clause on SQL Server platform

Without this patch a query would like like:
```
SELECT c0_.Country AS sclr0
FROM Continent c0_ WITH (NOLOCK)
WHERE c0_.Country = 38
GROUP BY sclr0
```
Using the column alias in the GROUP BY clause. However this is not allowed on SQL Server. References:
1. http://stackoverflow.com/a/3841804
2. http://technet.microsoft.com/en-us/library/ms189499.aspx (Logical Processing Order of the SELECT statement)

The correct query should be:
```
SELECT c0_.Country AS sclr0
FROM Continent c0_ WITH (NOLOCK)
WHERE c0_.Country = 38
GROUP BY c0_.Country
```
Changed GroupBy alias to real column name for all platforms and adjusted failing test accordingly. Has fallback in cases where real column name is not possible (example: Doctrine\Tests\ORM\Query\SelectSqlGenerationTest::testGroupBySupportsIdentificationVariable)
When the OptimisticLockingException is generated with the static function lockFailedVersionMismatch and the passed parameters are DateTime instances, the exception could not be thrown because the DateTime object is not implicitly converted to a string.
Merge pull request #793 from flip111/patch-2

Improved error messages in Paginator: LimitSubqueryOutputWalker
Merge pull request #788 from flip111/patch-3

Update DatabaseDriverTest.php
Removed unnecessary is_object() check
Merge pull request #807 from janbster/fix-optimisticlock

Fix for OptimisticLockingException
Made the code prettier :)
Merge pull request #801 from flip111/patch-4

Update SqlWalker.php fixed wrong GROUP BY clause on SQL Server platform
Second cache level POC
First round of refactory
Fix factory method name
refactoring region access tests
basically support for many to many collection
Refactoring tests
store cascade collections
refactoring collections store