fusermount: refuse unknown options

fusermount: refuse unknown options

Blacklists are notoriously fragile; especially if the kernel wishes to add
some security-critical mount option at a later date, all existing systems
with older versions of fusermount installed will suddenly have a security
problem.
Additionally, if the kernel's option parsing became a tiny bit laxer, the
blacklist could probably be bypassed.

Whitelist known-harmless flags instead, even if it's slightly more
inconvenient.