Fixed to the point that all unit tests pass again. (However, I get 4

"exception in thread" messages, one about a killed locker, and three
assertions.)  Details:

test/test_dbshelve.py:
- kill reference to InstanceType

test/test_basics.py:
- use // for int division
- use 'in' instead of has_key

dbshelve.py:
- fix bug in previous has_key fix, use self.db.has_key instead of self.has_key

dbtables.py:
- use 'in' instead of has_key

dbutils.py:
- fix bug in previous has_key fix, test for 'max_retries', not 'max_tries'