Allow directories as "paper files"

[Michael Banck]

From http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=531711:

For my papers and books I sometimes have supporting material, so I want to
have a directory instead of a PDF file in the "Document/File" property of that
document. It is possible to select a directory in the "Select A File" dialog,
although referencer makes it a bit difficult: descent into the directory you
want to select, type "." into the "Location" field and press the "Open"
button. I can then press the "Save" button in the "Document Properties"
dialog, and the next time I double click on the document in referencer
nautilus will open the directory (just like I want it). If I open the
"Document Properties" dialog again however, the "Document/File" property is
reset to "(None)". If I (instead of reopening the "Document Properties"
dialog) save the library, exit referencer, restart referencer and open the
"Document Properties" dialog of the document in question, the "Document/File"
property is _not_ reset. Saving alone without restarting does not prevent the
resetting of the property.

I'm not sure what is the intended behaviour here. Basically I can think of
two possibilities:

 1) Disallow directories completely. Then the trick I used to set a directory
    should not work to prevent surprises later.

 2) Allow directories. Then the resetting of the "Document/File" property
    should not happen (at least as long as the directory exists). Making it
    easier to select directories would be a bonus.

Naturally, I would prefer 2).

Thanks,
Jö.