* lisp/progmodes/compile.el (compilation--previous-directory): Simplify.
(compilation-next-error): Ensure the parse before we look at
compilation-message property.
* lisp/progmodes/m4-mode.el (m4-syntax-propertize): New var.
(m4-mode): Use it.
(m4--quoted-p): New function.
(m4-font-lock-keywords): Don't handle #..\n comments any more.
(m4-mode-syntax-table): Use punctuation syntax (according to m4 manual)
for most special characters.
src/ChangeLog: Fix a typo.