unique_case_insensitive attribute
removing the 'feature' that you couldn't AND queries together using the same field constraints.  For example qs.filter(x=1) qs.filter(x=2).
Dummy commit.
allow for duplicate AND'd queries and skip the tests that assume it's not possible
remove the deprecated mongoengine/base.py
Revert "allow for duplicate AND'd queries and skip the tests that assume it's not possible"

This reverts commit a165628f47832849e94047c5d4ef42b080141612.
use the simplification visitor, but dont raise an error for duplicate conditions