PR #4667 "fixed" issue #4622 by making all string literals Unicode in our SQL generation.

But it has been claimed that SQL Server cannot leverage indexes when comparing a Unicode literal or parameter against a non-Unicode column. For an example, see http://stackoverflow.com/questions/5828621/.

Rather than reopening #4622, I am creating a new issue to discuss the priority of sargability in this scenario on its own.

Whenever we decide to improve this we should verify in which scenarios the claim is valid and then we can avoid creating Unicode literals in those cases.