file-magic-chars is a string of characters that you would find
at the beginning of a file compressed in this way.
-Because of the way `call-process' is defined, discarding the stderr output of
-a program adds the overhead of starting a shell each time the program is
-invoked.
-
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