litle: support wiredump_device

By specifying a wiredump device, such as:

  ActiveMerchant::Billing::LitleGateway.wiredump_device = File.open('/var/tmp/litle.log', 'w')

the device will now be properly passed to the LitleOnline gem for logging.

The LitleOnline gem uses its own connection mechanism and the logging hook will be available
only in versions more recent than 8.15.

Testing Done: tested the integration with the Kill Bill Litle plugin (see http://kill-bill.org).

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
litle: support paypage registrations

Allow to pass a paypageRegistrationId in the store() call, instead of a
credit card.

Testing Done: tested the integration with the Kill Bill Litle plugin
(see http://kill-bill.org).

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>

Conflicts:
	lib/active_merchant/billing/gateways/litle.rb
litle: update error message

The recent changes require a version newer than 08.15.0 of the Litle gem.

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>