Add a reference to issue #39

[msporny]

Add a reference to issue #39.

[zkoch]

I don't think issues around registration belong in the paymentrequest spec. @ianbjacobs addresses this in his draft blog post, so I think that might be good enough for now.

[adrianhopebailie]

@zkoch I don't think this is about registration it's about integration between the user agent and a web based payment app.

@msporny For consistency, I think the issue markers for issues #50, #39 should follow a similar format as they both relate to payment app interface (one for native apps and the other for web based apps).

I would suggest the following text and would include this at an appropriate point in the section User Agent delegates payment request algorithm and possibly another reference in the complete() section as this refers to messages being passed back to the payment app.

Suggested text:

<p class="issue" data-number="39" title="It is unclear how the user agent will interface with 
a web-based payment app.">The architecture document suggests that payment apps may 
take numerous forms, including as web-based apps. This specification should describe how 
the user-agent will pass the payment request data and the complete signal to a web-based 
payment app and also how it will receive the payment response from the payment app.</p>

[msporny]

I would suggest the following text and would include this at an appropriate point in the section User Agent delegates payment request algorithm

Done, used your text and preferred location.

[adrianba]

Merged as 188ae18