CRM_Utils_String::munge()'s limit causing trouble with long group names

CRM_Utils_String::munge() (called by CRM_Utils_String::titleToVar()) limits the resulting var name to 31 characters. This forbids the users to create new groups that happen to share the first 31 characters with an existing group (as the groups' names would end up the same).

This seems like a fringe case, but actually came up today in our FISE works - we wanted to distinguish (and make them sort together) groups used for logically-grouping contacts and groups used for ACLs, so we prefixed the group names; this caused long group names that have common first part, and a clash on new group creation.

Assigning to Lobo for futher discussion with Micha? and me.