Bug 12164: (followup) keys expects a hash parameter

As of http://perldoc.perl.org/functions/keys.html we should avoid passing
a scalar parameter as it is not backwards compatible with squeezze's Perl
version (5.10).

Cite:
"Starting with Perl 5.14, keys can take a scalar EXPR, which must contain a
reference to an unblessed hash or array. The argument will be dereferenced
automatically. This aspect of keys is considered highly experimental. The
exact behaviour may change in a future version of Perl."

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>