[development] public vs private file transfer setting

[Stella Power]

Hi all,

I'm not sure if this is the correct place to ask, but a couple of issues, with
the same problem, have been logged against the 'avatar_selection' module which 
I maintain, and I don't know the solution.

For those of you who're not familiar with the avatar_selection module, it allows
users to pick their avatar image from a list of pre-configured images rather
than having to upload one.

Everything works correctly when the file transfer method is set to public, but
if you use the private setting, the images stop appearing.  I know there can be
problems if you switch between public and private settings but I made a clean
installation with the setting set to private and the problem persists.  I've had
a look at #92376 (why do image links point to /system/files/..?) but am no
closer to a solution.

The two issues are #138349 and #132277.

So if anyone can help me resolve this problem, it would be much appreciated!  Or
if I should be asking this some place else, please let me know.

Cheers,
Stella