Correcting invalid comment/documentation in config skeleton

According to
http://supervisord.org/configuration.html#program-x-section-settings
the default auto restart strategy is actually "unexpected". Correct me
if I'm wrong.

This commit also improves/clarifies the description for this property.

supervisor/skel/sample.conf

@@ -56,7 +56,7 @@ serverurl=unix:///tmp/supervisor.sock ; use a unix:// URL  for a unix socket
 ;umask=022                     ; umask for process (default None)
 ;priority=999                  ; the relative start priority (default 999)
 ;autostart=true                ; start at supervisord start (default: true)
-;autorestart=true              ; restart at unexpected quit (default: true)
+;autorestart=true              ; whether/when to restart (default: unexpected)
 ;startsecs=10                  ; number of secs prog must stay running (def. 1)
 ;startretries=3                ; max # of serial start failures (default 3)
 ;exitcodes=0,2                 ; 'expected' exit codes for process (default 0,2)