[web] fix AbstractSessionManager.clean_sessions (closes #5757240)
sessions were not closed if "last_usage_time = session.cnx.check()" actually
raises an AtributeError.
Tutorials
~~~~~~~~~
We present a few tutorials of different levels. The blog building
tutorial introduces one smoothly to the basic concepts.
Then there is a photo gallery construction tutorial which highlights
more advanced concepts such as unit tests, security settings,
migration scripts.
.. toctree::
:maxdepth: 1
base/index
advanced/index
tools/windmill.rst
textreports/index
dataimport/index