Potential for FastString uniques clashing with others
getUnique implementation for
FastString derives the unique from a sequential counter (starting at 0) associated with the global
FastStringTable. One can argue that this is okay since the
\x00 unique tag isn't used by any
UniqueSupply. However, if we allocate allocate enough
FastStrings we will overflow the zero-tag into regions of the tag-space used by other
UniqueSupplys. This will result in unique collisions.