REST

Ensure that RVterm() doesn't try to throw errors after unregistering its
error class

Tidy up test file to have no cyclic links in order to make h5dump
happier since H5Lvisit can't yet detect cycles

Update examples to now use RVinit()/RVterm() instead of
H5VLrest_init()/H5VLrest_term()

Remove all references to "H5VLrest"