Update Auto Compression mode for changes in option values.
If you change the options `jka-compr-compression-info-list',
`jka-compr-mode-alist-additions' or `jka-compr-load-suffixes'
outside Custom, while Auto Compression mode is already enabled
(as it is by default), then you have to call this function
afterward to properly update other variables. Setting these
options through Custom does this automatically.