[cwconfig] create a virtual "cubes" package _CubesImporter now handle import of "cubes" and return a virtual module so that "cubes" is always importable without having to create a __init__.py in CUBES_DIR and add CUBES_DIR/.. to sys.path. Drop custom code in setup.py used to create CUBES_DIR/__init__.py and drop now useless warning when cubicweb is installed in develop mode Update test_cubes_path() and ensure 'cubes.file' is not loaded before testing its import. This test seems to have mistakes because cubes are loaded automatically when discovering cw commands (cubes.<x>.ccplugin), not sure how this should be fixed definitely.

^build$
^dist$
\.egg-info$
^.tox$
^.cache$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
\.pybuild
debian/python-cubicweb
debian/*.log
debian/*.substvars
debian/cubicweb-doc
debian/cubicweb
debian/files

syntax: regexp
.*/data.*/database/.*
.*/data/ldapdb/.*
.*/data/uicache/
.*/data/libpython/cubicweb_.*/i18n/.*\.po
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/
^doc/_build
^doc/js_api/
test-results.xml