[pkg] Use Twisted < 16.0.0
We have some test failures with 16.0.0, such as:
- test_put_content (unittest_server.ETwistHTTPTC)
- test_base_url (unittest_httptest.TwistedCWAnonTC)
(grafted from 10c12f31d0fe38c2e8814176fc42bf2ea210efdf)
\.svn
^build$
^dist$
\.egg-info$
^.tox$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
syntax: regexp
.*/data.*/database/.*
.*/data/ldapdb/.*
.*/data/uicache/
.*/data/cubes/.*/i18n/.*\.po
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/
^doc/_build
^doc/js_api/