(hl-line-range-function, hl-line-face): Declare variables to avoid bytecomp warnings.
(hexl-mode-old-ruler-function): New variable.
(hexl-follow-line): Bind `hexl-mode-old-hl-line-range-function' and `hl-line-range-function' after `require' hl-line.
Then bind `hl-line-range-function' and `hl-line-face'.
Don't require frame. Don't use `with-no-warnings'.
(hexl-activate-ruler): Store the original value of `ruler-mode-ruler-function' to `hexl-mode-old-ruler-function'.
(hexl-mode-exit): Restore the original value of `ruler-mode-ruler-function'.