NH-2285 - Support for LockMode in linq provider

[OnurGumus]

reimplemented the ffix

[oskarb]

What bothers me a bit with this is that while the test cases hypothetically will execute the code and implicitly verify that there are no exceptions, they don't actually verify that the requested locking has been applied.

[oskarb]

It's unfortunately also vulnerable to caching issues:

var result1 = (from e in db.Customers
                     select e).SetLockMode(LockMode.Upgrade).ToList();
var result2 = (from e in db.Customers
                     select e).SetLockMode(LockMode.UpgradeNoWait).ToList();

If the above two statements are executed, the second query will reuse LockMode.Upgrade from the first query.

[oskarb]

I've rebased and submitted a version with improved test cases as PR #530. It shows some more work is required.