* config-daemon.ac: Move AC_ARG_ENABLE([daemon]...)...
* configure.ac: ... here.
When Nix programs are not found, error out only when
$guix_build_daemon is no.
* configure.ac: Compute and substitute `guix_localstatedir'.
* m4/guix.m4: Substitute `guix_system'.
* guix/config.scm.in (%store-directory, %store-directory, %system): New
variables.
* guix/store.scm (%nix-state-dir): Remove.
(%default-socket-path): Use %STATE-DIRECTORY as the default.
(%store-prefix): Use %STORE-DIRECTORY as the default.
* guix/utils.scm (%current-system): Default to %SYSTEM.
* test-env.in: New file.
* configure.ac: Add it to `AC_CONFIG_FILES' and `commands-exec'.
* config-daemon.ac: Set and substitute `GUIX_TEST_ROOT'.
* Makefile.am (SCM_LOG_COMPILER, SH_LOG_COMPILER): Use it in lieu of
`pre-inst-env'.
* daemon.am (test_root): Remove
(AM_TESTS_ENVIRONMENT): Remove `TEST_ROOT'.
(clean-local): Use $(GUIX_TEST_ROOT); make files writable before
removing them.guix_test_root
* tests/guix-daemon.sh: Remove `NIX_' variable settings; don't launch
`guix-daemon'.
* configure.ac: Change package name to "GNU Guix", and bug-report
address to `gnu-system-discuss@gnu.org'.
* doc/guix.texi: Replace "Guix" by "GNU Guix" in some places.
(Top, Introduction): Mention "for the GNU system".
* HACKING, README: Use "GNU Guix" instead of "Guix" in some places.
* configure.ac: Always show the result of checking for Nixpkgs. Don't
warn when Nixpkgs is not found.
* Makefile.am (AM_DISTCHECK_CONFIGURE_FLAGS): Remove `--with-nixpkgs'
flag.
* guix/utils.scm (%nixpkgs-directory): Use either the compile-time or
the run-time `NIXPKGS' environment variable.
* release.nix (jobs.tarball, jobs.build): Remove `--with-nixpkgs'
configure flag.
* README: Mark Nixpkgs as optional.
* distro/packages/databases.scm, distro/packages/guile.scm,
distro/packages/typesetting.scm: Change uses of `nixpkgs-derivation*'
to `nixpkgs-derivation', to avoid failing at compile-time.
