BUG: wmkdepend finds 'include' in multi-line comments (closes #784)

- the previous grammar used

      '/*' { fgoto comment; }

  to start processing multi-line comments and

      comment := any* :>> '*/' @{ fgoto main; };

  as a finishing action to return to normal lexing, but seemed not to
  have been triggered properly.

  Now simply trap in a single rule:

      '/*' any* :>> '*/';             # Multi-line comment

STYLE: use more compact dnl (delete to newline)

  OLD:   [^\n]* '\n'
  NEW:   (any* -- '\n') '\n'

  eliminates the intermediate state