[entity/optimization] Cache rset when entity.related is called with entities=False If fail to see why we couldn't cache in this case, while this is important for optimization reason: when doing a single HTTP request, some queries are done two or three times because of predicates / uicfg or alike. Also always store tuple and not list in the cache, because: * else we get some regression * and inconsistent result type (tuple or list) * and it simply feels better to cache an unmutable object.

etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances