* The default for ISABELLE_HOME_USER is now ~/.isabelle instead of the old ~/isabelle, which was slightly non-standard and apt cause surprises on case-insensitive file-systems, or when working with local copies of the Isabelle repository.
INCOMPATIBILITY, need to move existing ~/isabelle/etc, ~/isabelle/heaps, ~/isabelle/browser_info to the new place. Special care is required when using older releases of Isabelle. Note that ISABELLE_HOME_USER can be changed in Isabelle/etc/settings of any Isabelle distribution.
