There is nothing in this commit except for the changes made by
nix-shell -p nixfmt-rfc-style --run "nixfmt ."
If this has mucked up your open branches then sorry about that. You
can probably nixfmt them to match before merging
* [] is now [ ]
* {} is now { }
* commas in arglists go at end of line not beginning
In short, I ran the whole thing through nixfmt-rfc-style but only
accepted about 30% of its changes. I might grow accustomed to more
of it over time
this is step 1 of min-collect-garbage, no point implementing
deletion ourselves when rm -r exists
(arguably no point in implementing any of it, but this is the bit we
can't do efficiently in bourne shell - it means we're reading the
store-paths list once instead of grepping it afresh for every entry in
/nix/store/)
