[O] join on dates

[Samuel Wales]

just wondering if something like this already exists.  i was going to
do this with a keyboard macro, but i'm not sure if those are quite
powerful enough.  i won't be coding it.

i have subtrees "collection" and "results".  they both contain
inactive timestamps [with or without time or day of week].  all that
matters here is date.

i want to make sure that every collection is accounted for in results.
but results sometimes does not list the exact date [it's a few days
later when i receieve results].  or sometimes it lists it only in a
link description.

so i maybe want to do a join on date and then manually check.

i want 3 lists.  these lists should contain non-id links to the
relevant headers in a and b.  then i can manually check.

  1] headers that have the same date in both a and b
  2] headers that have a date in a but not b
  3] headers that have a date in b but not a