Model api does not fully work with memory

gt, lt such comparisons work fine when the db is configured as mysql, but wrong with memory.

eg,
There is a model called user is generated with age, name, birthday. Using

```
User.count({age:{gt:10}}, function(err, data) {....})
```

is fine under `compound c` but not `NODE_ENV="test" compound c`, while in `config/database.coffee` the configuration is set mysql as development env and memory as test env, respectively.

Look at the model API code handling comparison operators like 'gt' and 'lt'. The issue is that these work with MySQL but not with the in-memory database adapter. Start by examining the database configuration in config/database.coffee and the adapter implementations. Run the failing test in the test environment to reproduce the bug, then trace the query logic for the memory adapter.

Scritto dal modello di indicizzazione a partire dal testo della issue.