This ensures that Project.find_with_namespace returns a row matching
literally as the first value, instead of returning a random value.

The ordering here is _only_ applied to Project.find_with_namespace and
_not_ Project.where_paths_in as currently there's no code that requires
Project.where_paths_in to return rows in a certain order. Since this
method also returns all rows that match there's no real harm in not
setting a specific order either. Another reason is that generating all
the "WHEN" arms for multiple values in Project.where_paths_in becomes
really messy.

On MySQL we have to use the "BINARY" operator to turn a "WHERE" into a
case-sensitive WHERE as otherwise MySQL may still end up returning rows
in an unpredictable order.

Fixes gitlab-org/gitlab-ce#18603