Remove log4net dependency and update mongo driver.

Updated to Mongo 1.7 driver.
Removed log4net dependency in favor of just using trace messages.
Updated error messages.

We are using NLog and it seems like a bad idea to take on the log4net dependency in a generic component. Projects could be using any number of logging frameworks.

I'm not sure about updating the mongo driver to 1.7, but it appears that they made breaking changes in the 1.7 driver that make it necessary for projects using 1.7.