[rqlrewrite] rewrite doesn't need a solutions argument, always use the Select'ones
Also, do a copy systematically else it may lead to empty solutions depending on
the rewrite path.
Test case tentative included in the following changeset.
from cubicweb.schemas.base import in_group, CWSourceSchemaConfig
# copy __permissions__ to avoid modifying a shared dictionary
in_group.__permissions__ = in_group.__permissions__.copy()
in_group.__permissions__['read'] = ('managers',)
cw_for_source = CWSourceSchemaConfig.get_relation('cw_for_source')
cw_for_source.__permissions__ = {'read': ('managers', 'users'),
'add': ('managers',),
'delete': ('managers',)}