Use custom session name by default to avoid session corruption.

config/vufind/config.ini

@@ -159,9 +159,11 @@ lifetime                    = 3600 ; Session lasts for 1 hour
 ; Set the domain used for cookies (sometimes useful for sharing the cookies across
 ; subdomains); by default, cookies will be restricted to the current hostname.
 ;domain = ".example.edu"
-; This sets the session cookie's name. Only needed if you use session sharing over
-; multiple subdomains (see domain setting above) and you have multiple PHP apps.
-;session_name = VUFIND_SESSION
+; This sets the session cookie's name. Comment this out to use the default
+; PHP_SESS_ID value. If running multiple versions of VuFind (or multiple PHP
+; applications) on the same host, it is strongly recommended to give each a
+; different session_name setting to avoid data contamination.
+session_name = VUFIND_SESSION
 
 ; Please set the ILS that VuFind will interact with.
 ;