Fixes issue 331 by adding more __methodMissing functionality to the db object

- added a listCollections() prototype to the db object to call the same show collections
function as executing 'show collections' does directly
- Found all commands returned by the native mongo shells' db.help() command, and added these
as "reserved" keywords that should not be directy usable as collection names, because they
are not in the native mongo shell either