Add nvidia-smi tool and fix an embarrassing bug in a previous pull request of mine

nvidia-smi is nice because it's command line. It's already in the tarball for ages, no idea why we never installed it. :)

Also, yes indeed in my previous perf fix I forgot that -f must be in [ ] and didn't test properly that it still works (it did still build, but that's just because bash ignores such errors).