veriexec(4) maintenance

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

veriexec(4), and the fileassoc(9) API it uses internally, needs
maintenance and probably some serious rework to fix synchronization
problems on any MP and/or preemptible kernels (i.e., all x86 of the
past couple decades) with implications for any security properties it
is supposed to provide.

If anyone cares about veriexec(4) and would like to volunteer to take
this on, we can discuss what needs to be done and how to proceed.

(If not, we should maybe just delete it.)