Includes layout of both VBOXHGCMSVCFNTABLE and VBOXHGCMSVCHELPERS.
A service can work with these structures if major version is equal and minor version of service is <= version of the structures.
For example when a new helper is added at the end of helpers structure, then the minor version will be increased. All older services still can work because they have their old helpers unchanged.
Revision history. 1.1->2.1 Because the pfnConnect now also has the pvClient parameter. 2.1->2.2 Because pfnSaveState and pfnLoadState were added 2.2->3.1 Because pfnHostCall is now synchronous, returns rc, and parameters were changed 3.1->3.2 Because pfnRegisterExtension was added 3.2->3.3 Because pfnDisconnectClient helper was added 3.3->4.1 Because the pvService entry and parameter was added 4.1->4.2 Because the VBOX_HGCM_SVC_PARM_CALLBACK parameter type was added 4.2->5.1 Removed the VBOX_HGCM_SVC_PARM_CALLBACK parameter type, as this problem is already solved by service extension callbacks