Hash references on string now raise errors, not return nil.

Under Ruby 1.8 the syntax "foo"[:bar] would return nil, while Ruby 1.9 is
strict: it enforces that only numeric index arguments are acceptable and
raises an error when that precept is violated.

This means that a whole pile of specs that used to pass strings where
structured objects were accepted now blow up - because you can't request
arbitrary nonsense against their array dereference interface.

Signed-off-by: Daniel Pittman <daniel@puppetlabs.com>