Version 1.51

- Don't set the buffer 'modified' for :PrintDuplicates and :PrintUniques.
- Improve reporting of readonly buffers for :SubstituteExcept, :DeleteExcept, :SubstituteSelected, and :SubstituteSubsequent.
- FIX: Misplaced :continue in s:Collect() safety check; must :return out of factored out function.