MS SQL optimistic locking with timestamp/rowversion column

I tried to start support for MS SQL timestamp/rowversion column type.
A few issues I ran into:
- fetching binary columns does not work; they end up as strings (this is probably the cause for all problems I had!)
- the test for varbinary(max) fails

I added a few tests that should not fail. I couldn't find a way to make them pass. I am hoping for some help here.

I started with a new kind of optimistic locking. You can ignore that for now.

Sorry for any mistakes. This is my first pull request, so I probably broke some rules there.