Ensure model definition service returns nil if initialised with a nil session.
Modified tests so they all pass on a range of servers from 3.4.x to 5.0 (HEAD) and for both Enterprise and Community editions.

Also fixed some errors where the wrong parameter name is used in an assert which can lead to confusing crash reports.

Updated to latest snapshot of ObjectiveCMIS Library.
Updated version to 1.4-dev and updated to latest (0.5-dev) release of ObjectiveCMIS library.