Specify all of $(htmldir) as the doc.

Dependencies

• [2] JXLJS4RI release.nix: Make the HTML manual a Hydra build product.
• [3] Z45QO5BP hydra/release.nix: posthook -> postdist
• [4] UHMUHQMU hydra: fix tarball build, add pre suffix to tarballs
• [5] VXNVNOK5 release.nix: Install the manual under the right prefix.
• [*] T4LLYESZ * Nix expression for building Hydra.

Change contents

• replacement in release.nix at line 36
  [2.88]→[2.88:152](∅→∅)
  − echo "doc manual $out/share/doc/hydra/manual.html" >> \
  [2.88]

  [2.152]
  + echo "doc manual $out/share/doc/hydra" >> \