* daemon.am (libexec_PROGRAMS, nix_setuid_helper_SOURCES,
nix_setuid_helper_CPPFLAGS, nix_setuid_helper_LDADD): New variables.
* test-env.in: Set and export `NIX_SETUID_HELPER'.
* README (Installing Guix as non-root): New section.
* 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'.
* nix/scripts/list-runtime-roots.in: New file.
* config-daemon.ac: Add `AC_CONFIG_FILES' invocation for it.
* daemon.am (nodist_pkglibexec_SCRIPTS): New variable.
(AM_TESTS_ENVIRONMENT): Define `top_builddir'.
* tests/guix-daemon.sh: Export `NIX_ROOT_FINDER'.
* nix/sync-with-upstream: Substitute the path to the root finder in
libstore/gc.cc.
