[facets] support for `no_relation` on RelationFacet e.g. to filter en entities *without* a given relation as well as with a particular relation. Proposed or not by default according to relation cardinality. Also, try to guess i18nable properly from the schema by default.

usr/lib/python2.4/site-packages/cubicweb/
etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/run/cubicweb
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances