Mercury gateway updates

These are changes to the Mercury Gateway needed to pass a recent Mercury integration certification.   The Mercury Developer Integrations representative I worked with for the certification was Michael Mantineo, mmantineo@mercurypay.com.  The changes included in this PR are:

    * when parsing mercury response if ref_no is not present use invoice_no for ref_no

    * include AcqRefData for PreAuthCapture as well as reversal

    * default to partial auth deny
I agree that changing default behavior is a red flag.  However, while 
working through a recent Mercury gateway integration certification with 
Michael Mantineo mmantineo@mercurypay.com, he stated that defaulting 
partial auth to true was generally undesirable.  An example use case is: 
A merchant makes a sale for $10 but the buyer's card only has $5.  In 
general a merchant would want the transaction to fail for insufficient 
funds in this situation.  However, with partial auth true the 
transaction will result in a success but only $5 will have been charged. 
The merchant may not realize that they where only paid $5 because the 
transaction did not fail.

On 12/18/14 12:49 PM, Garett Shulman wrote:
>
> On 12/18/14 11:52 AM, Nathaniel Talbott wrote:
>>
>> In lib/active_merchant/billing/gateways/mercury.rb 
>> <https://github.com/Shopify/active_merchant/pull/1399#discussion-diff-22061981>:
>>
>> > @@ -90,7 +90,7 @@ def build_non_authorized_request(action, money, credit_card, options)
>> >            xml.tag! "Transaction" do
>> >              xml.tag! 'TranType', 'Credit'
>> >              xml.tag! 'TranCode', action
>> > -            if action == 'PreAuth' || action == 'Sale'
>> > +            if (action == 'PreAuth' || action == 'Sale') and options[:allow_partial_auth]
>>
>> I'm concerned that this is changing the default; now a flag has to be 
>> set to get the old behavior? In general I'm really dubious about 
>> adding another flag here. Why is it even needed?
>>
>> (Also, if you use |and| in Ruby you're generally gonna have a bad 
>> time. But not a big deal since whoever merges can change to |&&|.)
>>
>> —
>> Reply to this email directly or view it on GitHub 
>> <https://github.com/Shopify/active_merchant/pull/1399/files#r22061981>.
>>
>