Process isolation cannot be used for test execution because ReadPreference and similar driver classes cannot be serialized (see: PHPC-850).

This should have been done in 8dcc7784.

This property was missing from 8dcc7784.

This reverts the logic in 21b7d92a, which was to ignore an unsupported write concern for the duration of 1.x. Since the Collection helper methods do not supply a default write concern option if it is not supported, this change will only affect users that were explicitly passing a write concern and relying on the library to ignore it.

While a minor BC break, this changes makes findAndModify consistent with other write commands.