Problem: Illegal memory access with z= command. (Dominique Pelle)
Solution: Avoid case folded text to be longer than the original text. Use
MB_PTR2LEN() instead of MB_BYTE2LEN().
Problem: ]s does not move cursor with two spell errors in one line. (Manuel
Ortega)
Solution: Don't stop search immediately when wrapped, search the line first.
(Ken Takata) Add a test.
