The following is not a real solution, but it I think it would make the user
understand the necessary internals better:
Add a second dialog to the "User Installation" process that explains the user
Gimp's way of handling memory and allows him to choose the size of the
tile-cache-size and the location of the swap-file.
At this point the dialog should try to propose some reasonably alternatives:
Choices for the directory should be '~/.gimp/tmp' or the the result of
g_get_tmpdir(). And of course, the dialog should not give any default values
and will not go away until the user makes a decision.
To allow system-administrators to make this choices for their users, we skip
the dialog if the global gimprc already contains entries for these settings.
What do you think??