The string stored is now strlen(s)+1, with length 0 indicating NULL.
Increment savegame version for this new format.
Old savegames are fixed by assuming VAL_STRING should never be NULL.
This is mostly a lead-up to namespacing the Ad/Base folders, and then
possibly removing the prefixes from the files, it also has the added
benefit of getting rid of the odd case-typos that makes for issues
on platforms that don't ignore case.