Highball memory requirement (4GB) with common/{raise,safety}

Both test suites require more memory than my amd64 VM using
GENERIC-NODEBUG can provide and reliably panic it with OOM issues in
dtrace(4).

Some of the testcases fail, but this at least bypasses the panic behavior
on platforms that don't have enough resources

MFC after: 2 weeks
Discussed with: markj
Sponsored by: EMC / Isilon Storage Division