[ticket/12012] Correctly drop default value constraints
* nickvergessen/ticket/12012:
[ticket/12012] Move property to the top
[ticket/12012] Move MS SQL server comparison into a method
[ticket/12012] Fix docs in connection manager
[ticket/12012] Remove duplicated code (only the $sql are different)
[ticket/12012] Handle begin and commit transactions in tests
[ticket/12012] Drop and recreate indexes when removing columns
[ticket/12012] Add a unit test for removing a column with indexes
[ticket/12012] Add a unit test for changing the column type
[ticket/12012] Return SQL statements for index drop/create
[ticket/12012] Fix tools::mssql_get_existing_indexes() for SQL Server 2000
[ticket/12012] Drop and recreate indexes when changing a column on MSSQL
[ticket/12012] Fix query layout
[ticket/12012] Correctly drop default value constraints on MSSQL