bug#17587: 24.3; Input method french-prefix doesn't support oe ligature

[Christopher Schmidt]

Juliusz Chroboczek <jch@pps.univ-paris-diderot.fr> writes:
> Please give easy access to the « œ » ligature in french-prefix.

    C-h C-\ french-prefix RET


    Input method: french-prefix (mode line indicator:FR>)

    French (Français) input method with prefix modifiers

        effect   | prefix | examples
     ------------+--------+----------
        acute    |   '    | 'e -> é
        grave    |   `    | `a -> à
      circumflex |   ^    | ^a -> â
      diaeresis  |   "    | "i -> ï
       cedilla   | ~ or , | ~c -> ç   ,c -> ç
       symbol    |   ~    | ~> -> »   ~< -> «
        misc     |   /    | /o -> œ
                     ^^^^^^^^^^^^^^