- scoped traversals can now raise errors which contain the path of the
  current scope and an approximate source location based on preceding
  trace comments, if available
- initially, this new error messaging has only been added for the
  illegal size cast checks in the TypeOf and Cast conversions
- error suite tests can provide a verbose mode expected source location

- detect and forbid non-positive size casts
- detect and forbid negative struct pattern literal indices
- avoid invalid constant folding of negative based literals