Npgsqltypes files refactor

Hi Francisco,

Here's a patch that refactors a couple of the NpgsqlTypes/ files for better manageability.

This includes the commits in PR #59, but the refactor commit makes no functional changes.

I modified the VS2008, VS2010, and VS2012 project files.  2010 and 2012 test OK, but I don't have VS2008 anymore, so I couldn't test it.  No other project files were modified, so you'll have to fix up the mono build files.

-Glen