This adds a note to the man page to properly escape filters containing
spaces. It also fixes the unittests to reflect this.
One of the unittests contained an alternative syntax as discussed in
TW-1479 (#1505). It has been extracted into its own unittest and marked
as an expected failure because it is currently not supported.
This commit updates all tests to enforce the Python3 executable. This is
necessary because the `assertRegex` function we use was renamed to this
name only in Python 3.2 [1]
For reference:
s;/usr/bin/env python;/usr/bin/env python3;g
[1]: https://docs.python.org/3/library/unittest.html#unittest.TestCase.assertRegex
