Search filters in roundup can be transitive.  From hyperdb.py:

  ... e.g. you can search
  for all issues where a message was added by a certain user in
  the last week with a filterspec of
  {'messages.author' : '42', 'messages.creation' : '.-1w;'}

so in theory I should be able to submit a rest call as:

  issue?messages.author=42&messages.creation=.-1w

however the current code balks at that. Stating "messages.author"
isn't a valid property of issue. I wonder if we should rework the code
in rest.py that does:

  try: 
    prop = class_obj.getprops()[key]
  except KeyError:
    raise UsageError("Field %s is not valid for %s class."%(
          key, class_name))

to something like:

  try:
    prop = class_obj.getprops()[key.split('.')[0]]
  except: ...

This should result in:

   obj_list = class_obj.filter(None, filter_props)

getting filter_props like:

  {'messages.author', [1]}

which I think is properly handled.

Two questions:

  1) Does this seem the right thing to do? Should we support
     transitive searching in the rest interface? I don't see any
     reason it's not restful. It certainly beats searching
     messages?author=42&creation=.-1w then searching
     issues?messages=123,345,678 etc. (speaking of which
      curl 'https://....net/demo/rest/data/issue/?messages=1,2'
      returns all messages for some reason, so we may have
      another bug.)

  2) Does this seem to be the right way to implement it? Given a
     filter of link.link.link.property, should we check the whole link
     chain and validate the property, or do we just rely on filter
     raising an error if the filter is nonsense?