Merge branch 'master' into staging-next

There ver very many conflicts, basically all due to
name -> pname+version.  Fortunately, almost everything was auto-resolved
by kdiff3, and for now I just fixed up a couple evaluation problems,
as verified by the tarball job.  There might be some fallback to these
conflicts, but I believe it should be minimal.

Hydra nixpkgs: ?compare=1538299

pkgs/servers/sql/postgresql/ext/pg_topn.nix

@@ -14,7 +14,7 @@ stdenv.mkDerivation rec {
   };
 
   installPhase = ''
-    mkdir -p $out/{lib,share/extension}
+    mkdir -p $out/{lib,share/postgresql/extension}
 
     cp *.so      $out/lib
     cp *.sql     $out/share/postgresql/extension