0.20 will require some minor code upgrades.

1. Note the exception changes in HISTORY. Certain exceptions are now scoped under the BSON
module; if you're catching these, you will need to modify your code.

2. The BSON types are now scoped under the BSON module.

3. Note that mongo_ext no longer exists. The new gems are bson and bson_ext.

4. Indexes on GridFS chunks collections should be unique. If you have existing GridFS
collections, you should drop the current index and replace with a unique one. Before you do this,
make sure that index doesn't exist; no need to go through process unnecessarily.
If you do need to create the index, once you have the chunks collection, here are the commands you can run:

@chunks.drop_index('files_id_1_n_1')
@chunks.create_index([['files_id', Mongo::ASCENDING], ['n', Mongo::ASCENDING]], :unique => true)