See: PHPC-465, HHVM-129

See: PHPC-444, HHVM-117

Versions of MongoDB before 3.0 create a database when dropping the collection of a database that doesn't exist (as is done by the setUp() method).

Options can be passed directly to FindAndModify after any necessary translation/conversion.

We only use the writeConcern option if isset() return true, so we needn't complain about users passing a null value.