PHP-1034: Ensure MongoCommandCursor implements Iterator interface properly.
Merged pull request #645
PHP-1040: MongoCommandCursor::key() should not return _id field

This also updates aggregateCursor() tests to log query/getmore requests. New tests were added for getmores due to limit/batchSize relations, as well as an error test case for invalid batchSize options.
Add missing "proto" in MongoCommandCursor methods
Merge pull request #644
PHP-1041: Fix off-by-one error in MongoCommandCursor::key() indexes

The first result document should have index 0, not -1.
Merge pull request #644
PHP-1031: Implement MongoWriteBatch method to return current batch size

Added MongoWriteBatch->getItemCount() returning how many items are total
Added MongoWriteBatch->getBatchInfo() retrieving how many items are
in individual batch and its size (in bytes)
Don't throw exceptions on argument failures, as per cr feedback