DocViewSAXImporter relies on implementation detail wrt authorizable Id

upon user/group import the DocViewSAXImporter relies on the jackrabbit 2.x implementation that the authorizable id is encoded in the name of the corresponding node.

since oak 1.0 however this can be customized and there is no guarantee that the node name reveals the authorizable id (see http://jackrabbit.apache.org/oak/docs/security/user.html). in order to keep fvault compatible with oak this should be fixed.

proposed (but untested) patch attached.