[web/test] switch unittest_web from twisted to wsgi And make it pass on python3 while at it.

[devtools] add CubicWebWsgiTC Similar to CubicWebServerTC, except using wsgiref instead of twisted as an http server.

[web/test] return the hash of uploaded files in FileUploadTC instead of their contents json must be unicode, which doesn't go well with arbitrary file contents. Compute the file hash instead, as we know the hexdigest is (ascii) text.

[web/test] open() as a context manager

[web/test] json.loads expects text, not bytes

[wsgi] fix handling of multiple posted files We were only keeping the last received file.

[web/test] Reword doc string for fileupload ajaxfunc

[skeleton] do not import the __pkginfo__.py module to make cubes installable via setuptools When using a simple "import" statement, running 'python setup.py install' for a cube fails in a fresh virtualenv due to the fact the install of the dependencies (here cubicweb iteself) is done by the python process doing the cube's installation, so the __pkginfo__ module from the cube is already loaded (thus used) when installing cubicweb... So we apply the third technique from: https://packaging.python.org/en/latest/single_source_version.html

merge changes from 3.22.2

Added tag 3.22.2, debian/3.22.2-1, centos/3.22.2-1 for changeset 1b93ff37755b

[pkg] 3.22.2

[pkg] fix centos install

[datafeed] do NOT call commit in DataFeedXMLParser.process() (closes #10928592) and so, remove more useless code. Doing a commit in DataFeedXMLParser.process() is a bad idea because this method is called for every imported/updated entity, before handling deletions. So if we commit here, odds are quite high that we're violating some integrity constraint and end up with a ValidationError.

[schema] restore constraint checking when running on old sqlite Old sqlite3 doesn't provide CHECK constraint names in error messages, preventing us from translating a backend integrity error into a ValidationError. This was added in 2012, but the sqlite3 version in RHEL6 is older; so if we run on old sqlite, keep checking the constraints in python rather than only in SQL. Closes #10927494