make python 2.6 compatible

 - timedelta.total_seconds() is not available in python 2.6, compute
   internally

cc: @narenst @sginn
Set key to 0 before incrementing if it doesn't exist.
Setting redis[key][attribute] to 0 first before incrementing if it doesn't exist.
Merge with fixes for incr, decr, hincrby
Adding comparison tests and dependency on redis-py

- version numbers are now tracking redis-py version support
- bump up mockredis version to 2.7.2
- working on develop branch
use StrictRedis instead of Redis
Test with with Redis Server when possibe

Compare results of gets (defined in test_configuration) when redispy
and a local redis server is available.

TODO:

 - naming needs to be improved
 - currently the configuration is set for a very limited set of
   operations
Merge branch 'develop' of github.com:locationlabs/mockredis into develop