pdfs on PMC result list

pdf attachments were not showing up in the result lists of PMC, added them, and also did some cleanup and refactoring.

is there a way to have a real test for a result list? the test added just shows that the page would return multiple...
also `pdf` is always `true` and _technically_ the xpath doesn't have to evaluate to a single node (multiple `//div[@class="links"]`), so maybe above `var pdf = ZU.xpath(...)[0];` and `if (pdf) {` here.