Fix test warnings
Test the data being sent in auth.net calls in more detail
Fix message in moneris remote test
Payex: Use the right url for the purchase call

Heard from Payex: the purchase API call happens at the confined url in
production.  This fixes the 404 we were getting.
Braintree: Allow dynamic descriptors

Docs for it:
https://www.braintreepayments.com/docs/ruby/transactions/dynamic_descriptors

Braintree added the ability to also specify a descriptor url here:
https://github.com/braintree/braintree_ruby/commit/7a336acb9eecc4293e05af2c43a8f15848cf6f55#diff-bf222cdd67b742610b54bdf5774362fc

but Active Merchant is using an older version of the Braintree gem.  Not
sure if we want to upgrade to a more recent version.
add track_data support for Mercury
removed redundant lines
remote tests pass now
adds track_data remote tests
Remove supported countries from bogus gateway
Update changelog

I neglected to do so when merging the previous pull requests.  I'd
grown accustomed to others updating the changelog as the PR was brought
in.  Time to step up!
Openpay: Add support for device session id

This is for Openpay's anti-fraud tool.  Docs for it:

http://www.openpay.mx/docs/api/#con-id-de-tarjeta-o-token

Closes #1411
Merge pull request #1412 from Shopify/remove_supported_cpuntries_from_bogus_gateway

Remove supported countries from bogus gateway
removed AVS/CVV from track data request
Merge pull request #1407 from Shopify/fix_moneris_message_in_test

Fix message in moneris remote test
Merge pull request #1406 from Shopify/add_more_auth_net_tests

Test the data being sent in auth.net calls in more detail
Redsys: Add support for verify

Cleaned up some tests while I was in there.
Redsys: Handle unsupported currencies

Previously, if a customer specified a currency that the Redsys adapter
didn't yet understand, it would raise a somewhat obtuse error:

TypeError: no implicit conversion of nil into String

Now we raise an ArgumentError with an appropriate message.
unless instead of if
Merge pull request #1410 from Shopify/track_data_mercury

add track_data support for Mercury