tests: make test-manifest.py portable to Python 3
Lots of b prefixes here, and https://bugs.python.org/
issue29714 means
that this test is still very broken on Python 3.6 and 3.6.1, but 3.6.2
should things (based on testing using tip of the 3.6 branch from git).
#cleanup-only
http://example.com/no/anchor, branches: (None, [])
http://example.com/an/anchor, branches: ('foo', [])
http://example.com/no/anchor/branches, branches: (None, ['foo'])
http://example.com/an/anchor/branches, branches: ('bar', ['foo'])
http://example.com/an/anchor/branches-None, branches: ('foo', [])
http://example.com/, branches: (None, [])
http://example.com/, branches: (None, [])
http://example.com/, branches: ('foo', [])