highlight-changes and french-prefix input method

[David Kuehling]

In Emacs 21.1.1 I just found another bug concerning the `french-prefix'
input method when used together with highlight-changes mode.

Here's how to reproduce the bug:

* type "abcdefghijklm"
* M-x set-input-method <ret> frech-prefix <ret>
* M-x highlight-changes-mode <ret>
* move point to inside the previously typed word "abcdefghijklm"
* enter french characters "'e`e"

the result will then be something like "abcdefééèèghijklm" (accented
characers are doubled).

Here's the corresponding dribble file:

abcdefghijklm
0x8000078set-input-method<return>french-prefix<return><left><left>
<left><left><left><left>0x8000078highlight-changes-mode<return>'e`e

                                                        David Kühling