Variable: jka-compr-mode-alist-additions

List of pairs added to `auto-mode-alist' when installing jka-compr.
Uninstalling jka-compr removes all pairs from `auto-mode-alist' that
installing added.

If you set this outside Custom while Auto Compression mode is
already enabled (as it is by default), you have to call
`jka-compr-update' after setting it to properly update other
variables. Setting this through Custom does that automatically.