Setting Server Base Url to have a different context causes HTML exports to store two files for the one image attachment.

Steps to reproduce.

1) Install a standalone copy of confluence. Set the context to be "/confluence" so you access the local instance as "http://localhost:8080/confluence".

Now suppose the customer has setup a Web server such as Apache that accesses this server using the URL "http://my.confluence.com", thus has no context. (You don't need to setup Apache to reproduce this, simply keep following the below steps.

2) Change you Server base URL to be "http://my.confluence.com"

3) Export a space (which has attachments, one of which is an image attachment and is displayed on the page) in html format. You will find that the image attachment is located within the export in both export/confluence/download/attachment/.../.../image.jpg and export/download/attachment/.../../image.jpg.

To reproduce this behaviour more easily I have included a space export.
After completing step 1,2 above, do the following.
a) Import the export into your 2.7.3 install.
b) export the space as a html file.

Customers should be able to have two different contexts and still not have a duplicate files in the export.