[dataimport] extid must be a bytes object

[dataimport] import StringIO from io

[dataimport] fix ucsvreader for python3 The csv module in python3 wants str, so use a StreamReader to feed csv.reader and don't decode the output

[server/test] import StringIO from io on python3 Don't change the import for python2, as we print a mix of unicode and str.

[server/datafeed] drop URLLibResponseAdapter.info I don't know where it's used

[devtools] pass a key to sort() method python3 dicts are not comparable

[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())