Fix how SQL Server 2008+ stores dates

Actually Nuxeo VCS use the datetime column type to store dates. The problem is that type does not take into account the timezone set with the date, and as a consequence, setting a date with any of these values

2013-07-10T18:30:00.436+03:00

or

2013-07-10 18:30:00.436

stores the same value !

Since SQL Server 2008, a new type datetimeoffset was introduced that may help to improve the storage of dates from Nuxeo