Before that, calls to 'HashSink::currentHash()' would eventually lead to
a segfault because the underlying gcrypt handle has been closed. (Note
that this method is only used via 'importPaths' and 'exportPath', though.)
* nix/libutil/gcrypt-hash.hh (struct guix_hash_context): Add a
constructor and a copy constructor; move out of 'extern "C"'.
* nix/libutil/gcrypt-hash.cc (guix_hash_final): Clear 'md_handle' upon
exit.
* nix/sync-with-upstream (top_srcdir): Change hash.{cc,hh} to read
'struct Ctx' instead of 'union Ctx'.
* 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.
