Merge branch 'nix' into 'master'.

nix/AUTHORS

nix/COPYING

nix/boost/assert.hpp

nix/boost/format.hpp

nix/boost/format/exceptions.hpp

nix/boost/format/feed_args.hpp

nix/boost/format/format_class.hpp

nix/boost/format/format_fwd.hpp

nix/boost/format/format_implementation.cc

nix/boost/format/free_funcs.cc

nix/boost/format/group.hpp

nix/boost/format/internals.hpp

nix/boost/format/internals_fwd.hpp

nix/boost/format/macros_default.hpp

nix/boost/format/parsing.cc

nix/boost/throw_exception.hpp

nix/libstore/build.cc

nix/libstore/derivations.cc

nix/libstore/derivations.hh

nix/libstore/gc.cc