Move entity cache from web.request.ConnectionCubicWebRequestBase to repoapi.ClientConnection ResultSet._build_entity relies on an entity cache to avoid going round in circles (stack overflow due to infinite recursion) e.g. in a postcreate script. Clear the cache at commit/rollback time to avoid unexpected side effects; and explicitly clear the cache in a few tests where we mix ORM and RQL using the same connection.

\.svn
^build$
^dist$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
syntax: regexp
.*/data/database/.*\.sqlite
.*/data/database/.*\.config
.*/data/database/tmpdb.*
.*/data/ldapdb/.*
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/
data/pgdb/