unit test added for altering a column's default where the column name is...

... a keyword - fails on mssql:
````

Exception : [Doctrine\DBAL\DBALException] An exception occurred while executing 'ALTER TABLE column_keyword_test DROP CONSTRAINT DF_D3D4D2F1_4BF2EAC0':

SQLSTATE [42000, 3728]: [Microsoft][SQL Server Native Client 11.0][SQL Server]'DF_D3D4D2F1_4BF2EAC0' is not a constraint.
SQLSTATE [42000, 3727]: [Microsoft][SQL Server Native Client 11.0][SQL Server]Could not drop constraint. See previous errors.

With queries:
5. SQL: 'ALTER TABLE column_keyword_test DROP CONSTRAINT DF_D3D4D2F1_4BF2EAC0' Params: 
4. SQL: 'SELECT    col.name,
                          type.name AS type,
                          col.max_length AS length,
                          ~col.is_nullable AS notnull,
                          def.definition AS [default],
                          col.scale,
                          col.precision,
                          col.is_identity AS autoincrement,
                          col.collation_name AS collation,
                          CAST(prop.value AS NVARCHAR(MAX)) AS comment -- CAST avoids driver error for sql_variant type
                FROM      sys.columns AS col
                JOIN      sys.types AS type
                ON        col.user_type_id = type.user_type_id
                JOIN      sys.objects AS obj
                ON        col.object_id = obj.object_id
                JOIN      sys.schemas AS scm
                ON        obj.schema_id = scm.schema_id
                LEFT JOIN sys.default_constraints def
                ON        col.default_object_id = def.object_id
                AND       col.object_id = def.parent_object_id
                LEFT JOIN sys.extended_properties AS prop
                ON        obj.object_id = prop.major_id
                AND       col.column_id = prop.minor_id
                AND       prop.name = 'MS_Description'
                WHERE     obj.type = 'U'
                AND       (obj.name = 'column_keyword_test' AND scm.name = SCHEMA_NAME())' Params: 
3. SQL: 'ALTER TABLE column_keyword_test ADD CONSTRAINT DF_D3D4D2F1_ACF51D19 DEFAULT 23 FOR [select]' Params: 
2. SQL: 'CREATE TABLE column_keyword_test ([select] INT NOT NULL)' Params: 

Trace:
C:\projects\doctrine\dbal\lib\Doctrine\DBAL\Connection.php:988
C:\projects\doctrine\dbal\lib\Doctrine\DBAL\Schema\AbstractSchemaManager.php:971
C:\projects\doctrine\dbal\lib\Doctrine\DBAL\Schema\AbstractSchemaManager.php:612
C:\projects\doctrine\dbal\lib\Doctrine\DBAL\Schema\SQLServerSchemaManager.php:232
C:\projects\doctrine\dbal\tests\Doctrine\Tests\DBAL\Functional\Schema\SchemaManagerFunctionalTestCase.php:619
C:\projects\doctrine\dbal\vendor\phpunit\phpunit\PHPUnit\Framework\TestCase.php:976
C:\projects\doctrine\dbal\vendor\phpunit\phpunit\PHPUnit\Framework\TestCase.php:831
C:\projects\doctrine\dbal\vendor\phpunit\phpunit\PHPUnit\Framework\TestResult.php:648
C:\projects\doctrine\dbal\vendor\phpunit\phpunit\PHPUnit\Framework\TestCase.php:776
C:\projects\doctrine\dbal\vendor\phpunit\phpunit\PHPUnit\Framework\TestSuite.php:775
C:\projects\doctrine\dbal\vendor\phpunit\phpunit\PHPUnit\Framework\TestSuite.php:745
C:\projects\doctrine\dbal\vendor\phpunit\phpunit\PHPUnit\TextUI\TestRunner.php:349
C:\Program Files (x86)\PHP\v5.3\pear\PHPUnit\TextUI\Command.php:176
C:\Users\deepdiver\AppData\Local\Temp\ide-phpunit.php:268
C:\Users\deepdiver\AppData\Local\Temp\ide-phpunit.php:506

#0 C:\projects\doctrine\dbal\vendor\phpunit\phpunit\PHPUnit\Framework\TestCase.php(946): Doctrine\Tests\DbalFunctionalTestCase->onNotSuccessfulTest(Object(Doctrine\DBAL\DBALException))
#1 C:\projects\doctrine\dbal\vendor\phpunit\phpunit\PHPUnit\Framework\TestResult.php(648): PHPUnit_Framework_TestCase->runBare()
#2 C:\projects\doctrine\dbal\vendor\phpunit\phpunit\PHPUnit\Framework\TestCase.php(776): PHPUnit_Framework_TestResult->run(Object(Doctrine\Tests\DBAL\Functional\Schema\SQLServerSchemaManagerTest))
#3 C:\projects\doctrine\dbal\vendor\phpunit\phpunit\PHPUnit\Framework\TestSuite.php(775): PHPUnit_Framework_TestCase->run(Object(PHPUnit_Framework_TestResult))
#4 C:\projects\doctrine\dbal\vendor\phpunit\phpunit\PHPUnit\Framework\TestSuite.php(745): PHPUnit_Framework_TestSuite->runTest(Object(Doctrine\Tests\DBAL\Functional\Schema\SQLServerSchemaManagerTest), Object(PHPUnit_Framework_TestResult))
#5 C:\projects\doctrine\dbal\vendor\phpunit\phpunit\PHPUnit\TextUI\TestRunner.php(349): PHPUnit_Framework_TestSuite->run(Object(PHPUnit_Framework_TestResult), false, Array, Array, false)
#6 C:\Program Files (x86)\PHP\v5.3\pear\PHPUnit\TextUI\Command.php(176): PHPUnit_TextUI_TestRunner->doRun(Object(PHPUnit_Framework_TestSuite), Array)
#7 C:\Users\deepdiver\AppData\Local\Temp\ide-phpunit.php(268): PHPUnit_TextUI_Command->run(Array, true)
#8 C:\Users\deepdiver\AppData\Local\Temp\ide-phpunit.php(506): IDE_Base_PHPUnit_TextUI_Command::main()
#9 {main}