Clean up hint command.
Parse Content-Disposition headers more relaxed.

Before, we got an unhandled ValueError if there were multiple spaces in a
filename.

Instead of ignoring such a header altogether, we now add relaxed=True which
still tries to get the filename in this situation (and with a semicolon at the
line end).

Because the parser is also more relaxed in that second case, we mark a test as
expected failure.