Make test-memwipe work better on OpenBSD
Where "work" means access freed buffers without exploding.
It currently segfaults 100% of the time but it could be "fixed" by setting the malloc.conf options in the program to turn off some of the protections.
's' will turn off malloc canaries (among other things). This stops it segfaulting. 'c' would do the same thing but would break on releases older than 5.9 which didn't have that option. 's' also means any new protections that are enabled by default will be turned off, which might help this keep working in the future.
Junking has two levels, so it needs 2x 'j' to guarantee it's turned off. This makes the warning about unreliable results go away.
Freelist and unmap protection aren't on by default but it will crash if it is, so a 'u' and 'f' will ensure it's off (it does nothing if it's already off).