Allow users to reproduce builds on their own systems

You can now do:

  bash <(curl http://hydra-server/build/1238757/reproduce)

to download and execute a script that reproduces a Hydra build
locally.  This script fetches all inputs (e.g. Git repositories) and
then invokes nix-build.

The downloaded sources are stored in /tmp/build-<buildid> and reused
between invocations of the script.

Any additional command line options are passed to nix-build.  So

  bash <(curl http://hydra-server/build/1238757/reproduce) --run-env

will drop you in a shell where you can interactively hack on the
build, e.g.

  $ source $stdenv/setup
  $ set +e
  $ unpackPhase
  $ cd $sourceRoot
  $ configurePhase
  $ emacs foo.c &
  $ make

and so on.
hydra-module.nix: update hydra-check-space for systemd

The "stop" alias is not available to this script when run from cron.
Merge pull request #84 from peti/update-hydra-check-space-for-systemd

hydra-module.nix: update hydra-check-space for systemd
Fix the test
hydra-eval-guile-jobs: Use `--fresh-auto-compile'.

* src/script/hydra-eval-guile-jobs.in (main): Run `guile' with
  `--fresh-auto-compile'.
Merge remote-tracking branch 'upstream/master'
Implemented upgrade transition to schema 12 for sqlite DBs