[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.

^build$
^dist$
\.egg-info$
^.tox$
^.cache$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
\.pybuild
debian/python-cubicweb
debian/*.log
debian/*.substvars
debian/cubicweb-doc
debian/cubicweb
debian/files

syntax: regexp
.*/data.*/database/.*
.*/data/ldapdb/.*
.*/data/uicache/
.*/data/libpython/cubicweb_.*/i18n/.*\.po
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/
^doc/_build
^doc/js_api/
test-results.xml