Silent failure when unable to access the temporary directory

[pjcdawkins]

For example, if originally installed as root, and then run as non-root, the CLI may fail with no output, because it can't access its temporary files:

[pjcdawkins]

This is probably more general - the debug env var probably shouldn't be needed if the error is a fatal one

[akalipetis]

If the directory exists, but we don't have access to it, we could start iterating until we find an available suffix (-1, -2, etc).

This will probably resolve #47, as each user will get their directory.