Fix AttributeError for "lang" on repo/client connections
This is a regression introduced by b48020a80dc3, which removed call to
set_language from the `req._set_user` method. This is fine, but we still want a
language on connections, so we've to handle it if necesary in
Connection.__enter__ (i.e. once connection is properly open).
When using pyramid front-end, which has a users cache, we've to cache its
language as well because we must not access its preferred_language method since
it's not bound to a proper connection.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/html/index.html
Files: /usr/share/doc/cubicweb-documentation/html/*