Optimise repo_connect by skipping authenticate_user
The authentication being handled by pyramid itself, going through the
authentication stack to recreate the temporary session at each request is very
costly.
On my desktop, for a mostly static front page, the total time for delivering
the page drops from 100ms to 47ms.
syntax: glob
*.pyc
*.swp
*.egg-info
pyramid_cubicweb/tests/data/database