Work around 9P corruption on 32-bit

Dependencies

• [2] WDNDBFSG 32-bit qemu can only do 2047 MB
• [3] LZVO64YG Merge in the first bits of the API work
• [4] 7C6HSXUQ * Start of a regression test for Hydra.
• [*] T4LLYESZ * Nix expression for building Hydra.

Change contents

• replacement in release.nix at line 178
  [3.126]→[3.126:194](∅→∅)
  − let hydra = builtins.getAttr system build; in # build.${system}
  [3.126]

  [3.194]
  + let hydra = builtins.getAttr system build; in # build."${system}"
• edit in release.nix at line 186
  [2.44]

  [3.501]
  + boot.kernelPackages = pkgs.linuxPackages_3_10;