range for BETWEEN typo fixed


extra/perror.c:
  meaningless error message fixed
heap/hp_rfirst.c:
  Bug #6748 heap_rfirst() doesn't work (and never did!)
mysql-test/r/heap.result:
  Bug #6748 heap_rfirst() doesn't work (and never did!)
mysql-test/r/range.result:
  range for BETWEEN typo fixed
mysql-test/t/heap.test:
  Bug #6748 heap_rfirst() doesn't work (and never did!)
sql/handler.cc:
  Bug #6748 heap_rfirst() doesn't work (and never did!)
sql/sql_select.cc:
  range for BETWEEN typo fixed