Creates initial mongodb driver and 'mongo' driver alias

- no associations yet (no JOINS supported);
- no tests done, only single queries (find, update and insert) but all
others should just work
Removes debug log lines
Adds mongodb support to test common.js
Fixes previous commit about mongodb support

Cannot use alias
Updates mongodb driver to pass Model.count tests
Updates mongodb Driver.drop to avoid returning error (when no collection is found)
Merge branch 'master' of github.com:dresende/node-orm2 into mongodb

* 'master' of github.com:dresende/node-orm2:
  Check for the existence of this.config.query.
  Add where sql doco
  Update tests to document 'where' not 'find'
  Allow querying chainfind with sql conditions
Passes connection settings to database drivers

Drivers can change settings if needed. This is needed for example for
now to mongodb driver change primary key to "_id"
Updates mongodb driver to support DBRef and change primary key settings
Changes Model to accept string as a Shell Model id (for mongo this is necessary)
Removes previous mongodb.convertToDB code about DBRefs
Changes hasOne tests to be database agnostic (don't use instance.id, use instance[model.id])

This changes makes mongodb successfully pass this tests automatically
Changes Model.extendsTo to avoid using Model.get(num)

Uses Model.find().first() since there's only one item in Model and this
way mongodb works directly
Updates Instance to check for new one_assoctions.field structure for required properties

SGBD tables would enforce required values but mongodb for now does not,
so this should be done before even going to database
Changes hasOne required tests to define an association field
Updates mongodb driver.count() to use convertToDB in conditions (same as driver.find())
Ignores hasMany and Model.aggregate() tests for mongodb
Updates some tests to avoid depending on "id" as primary key
Updates mongodb driver.remove() to use convertToDB
Adds mongodb support for ORM query comparators

The only one that I'm not sure is ok is LIKE => $regex