Changes
Mutex fixes (especially on Windows) and improvements (failures throw exceptions).
New Cursor::info() function, which gives the query, fields, namespace, limit, and
skip (by Cesar Rodas)
Added safe option for remove, update, batch, and gridfs insert methods.
Added keyf option for MongoCollection::group: pass a MongoCode instance as the
grouping key to use keyf.
Added comparison handlers for MongoId, allowing you to use, for example, in_array
with MongoIds.