[[plugins/aggregate]] takes a name parameter that specifies a global name
for a feed. This causes some problems:

* If a site has multiple pages that aggregate, and they use the same
  name, one will win and get the global name, the other will claim it's
  working, but it's really showing what the other aggregated.
* If an aggregate directive is moved from page A to page B, and the wiki
  refreshed, aggregate does not realize the feed moved, and so it will
  keep aggregated pages under `A/feed_name/*`. To work around this bug,
  you have to delete A, refresh (maybe with --aggregate?), and then add B.

Need to find a way to not make the name be global. Perhaps it needs to
include the name of the page that contains the directive?
