Prepare "Filter" to be jQuery UI 1.10 compliant

Hello Eric,
_I apologize in advance for my english, I'm a french dude ..._

Well first, thank you for this plugin ... It's great, works perfectly and seems to be part of the real jQuery UI itself (!).

I was working on a project using Multiselect and the Filter plugin under jQuery UI version 1.9. When I tried to avoid old 1.8 features with the `$.uiBackCompat` setting, I had some errors coming from the Filter plugin ...
So here it is, I fixed it and, as far as I know, it seems to work with all versions of jQuery just as usual ...

**The modifications**

Nothing very difficult:

-   I just changed the `data('multiselect')` to `data('echMultiselect')` to retrieve the instance, which is the new usage,
-   and correct a strange call of function `_self._toggleState` that doesn't exist, into `instance._toggleState` that seems to be the correct call
-   I also made a simple correction on the french strings (a missing accent).

I did NOT rebuild the minified version of the Filter plugin.

Let me know if I made mistakes or what ???

And thank you again ;)