clarify ID address spacing of Object IDs

Section 2.2.1.1 (ID Property) lines 241-244 state:

While all CMIS identities share the same Property-Type, they do not necessarily share the same address space. (So a particular repository implementation MAY use separate address spaces for different kinds of identity, and may perform different validity checks in a way that is outside the scope of the CMIS interfaces.)

Yet later in section 3.4.5 getAllowableActions we see:

3.4.5 getAllowableActions
Description: Gets the list of allowable actions for an Object (see "3.1.3 Allowable Actions" section).
3.4.5.1 Inputs
Required:
• ID repositoryId: The identifier for the Repository.
• ID objectId: The identifier for the object

Based on the allowable actions described in section 2.8.5.2 (line 638), This implies that at least the following objectIDs must be in the same namespace: Document object id, Folder object id, relationship object id, policy object id in order for the system to distinguish between them.