[postcreate] properly set is_instance_of for bootstrap entities Entities created before CWEType itself need the is/is_instance_of relations created later. We were actually only inserting "is". Closes #7656606.

[migration] re-try without print_function when compiling a script fails As part of the python3 porting we added the __future__.print_function import to cubicweb.migration. That started affecting all migration scripts it runs, which may not be prepared. So if compiling a script results in SyntaxError, try again without the print_function flag. Closes #7935030

[test] do not overwrite user's CW_CUBES_PATH in unittest_migration Currently when you rely on your CW_CUBES_PATH environment variable to locate cubes necessary for cubicweb's tests, the migration test crashes because it overrides the env var.

[server/test] dict.itervalues() → iter(dict.values())

make sync_schema_props_perms(<computed rtype>) work as expected It currently ends up with an ExecutionError while we want to synchronize permissions. This makes 3.21.1 migration of any application using computed relation crashing. Also, remove pre 3.6 compat code in hooks that prevent living schema update on computed relation's permission changes.

[web/http_headers] use classmethod decorator

[schema] use classmethod decorator

[devtools] delete postgresql socket directory after killing the server ... or when failing to start it.

[skel] stop deleting cubes egg-info It doesn't hurt and provides some metadata.

[dataimport] Update doc to reflect new API relate() looks deprecated.