Use global variable for file listing rather than calling document() to get the DRI again

This fixes an issue where data package pages may get stuck while loading.  The theme XSL would generate a second request for the resource it was transforming, and this was sometimes causing the pipeline to deadlock if the document was not already cached.

Instead, since the original DRI document is the starting point, this change simply captures the file listing in a global variable so that it can be recalled by the appropriate template.