Fix broken remote tests.
Send currency to Authorize.net so that it can be used in both CA and UK.
SagePay: Add support for GiftAidPayment

This is an optional flag to indicate that the payment is a Gift Aid
charitable donation and the customer has agreed to donate the tax.

Closes #568.
Fix format() with string input error

The documentation on http://activemerchant.org uses strings when instantiating `ActiveMerchant::Billing::CreditCard`. However, if '08' or '09' is used, it can cause an error as sprintf assumes it is doing an octal conversion.

Failing test case:

```
test_should_format_number_by_rule(CreditCardFormattingTest):
ArgumentError: invalid value for Integer(): "08"
    /Users/gabebug/github/active_merchant/lib/active_merchant/billing/credit_card_formatting.rb:13:in `sprintf'
    /Users/gabebug/github/active_merchant/lib/active_merchant/billing/credit_card_formatting.rb:13:in `format'
    /Users/gabebug/github/active_merchant/test/unit/credit_card_formatting_test.rb:17:in `test_should_format_number_by_rule'
    /Users/gabebug/.rvm/gems/ruby-1.9.3-p286/gems/mocha-0.11.4/lib/mocha/integration/mini_test/version_230_to_262.rb:28:in `run'
```
Add partial captures to wirecard gateway
* Added add_amount function to add amount for capture and transaction
* Changed authorize method to use the wirecard preauthorization api
  * Partial captures don't work with 'authorize'
  * Preauthorize allocates funds for the merchant
* Changed capture_authorization action to just capture
  * capture_authorization is an invalid function for partial captures
* Added remote tests and unit tests
  * Also changed the mocked response to reflect changes in api functions
  used
* Changed permitted_transactions to reflect changes
Removed a comment that no longer applied.
Merge branch 'master' of github.com:Shopify/active_merchant into rlb-wirecard_partial_capture
An attempt to fix failing tests on the Ci server caused by whitespace.
Update the CHANGELOG
Merge pull request #571 from Shopify/rlb-wirecard_partial_capture

Capture partial payments for the wirecard payments
Merge pull request #569 from Shopify/authorize-net-can-uk

Add support for Authorize.net in CA and UK
Fix incorrect test card numbers for beanstream amex.
Just fixes syntax highlighting in Sublime Text.
 # symbol needs to be stripped from paflow link description field
A couple minor fixes
Merge pull request #573 from jduff/fix_payflow_link_description_field

 # symbol needs to be stripped from payflow link description field
Add Pin gateway

http://www.pin.net.au/

Closes #565.
Balanced: Added support for on_behalf_of_uri

Balanced Payments offers the ability to associate a merchant with a
transaction on the capture of a previously authorized transaction. The
parameter is called on_behalf_of_uri. The parameter is not echoed back
in their response.

Closes #566.
Litle: Add support for passing an order_source

See orderSource in the Litle XML Reference Guide section 4.151

Closes #572.
Add MerchantWarrior gateway

http://www.merchantwarrior.com/

Closes #574.