* lib/Automake/Variable.pm (hook): Use $$ as prototype, not $&.

* lib/Automake/Variable.pm (hook): Use $$ as prototype, not $&.
Perl 5.6.0 will not accept a reference sub reference for the
latter.
* automake.in (var_SUFFIXES_trigger): Adjust registration via
Automake::Variabke::hook.
(handle_texinfo_helper): Make sure `inner_expand => 1' appears
on one line, so that Perl 5.6.0 does not complain about
inner_expand being a bare identifier.