So, it might be called sha1sum, or on some other OS, it might be called
sha1. It might be hidden away off of PATH on that OS. That's just expected
insanity; UNIX has been this way since 1980's. And these days, nobody even
gives the flying flip about standards that we briefly did in the 90's
after the first round of unix wars.
But it's the 2010's now, and we've certainly learned something.
So, let's make it so sometimes sha1 is a crazy program that wants to run as
root so it can lock memory while prompting for a passphrase, and outputting
binary garbage. Yes, that'd be wise. Let's package that in major Linux
distros, too, so users can stumble over it.
Don't check if configure indicated checks won't work. This should fix a
FTBFS on mipsel, where configure correctly detects the checks won't work,
while garbage is returned for disk space info at git-annex runtime. It also
means that, when built via cabal, disk space checks are not enabled,
unfortunatly.
