Accentuated characters break the link to a user

[Averell7]

Although this bug is related to : Slug transliteration #194, I create a new issue because it is really different, it is a question of transliteration only (I may be wrong on that point)

Suppose the user : Béatrice
In a message, you want to create a link to her message :
@béatrice#12

In the text, you will see : @béatrice#12, and the link is not created.

The reason is transliteration.
Transliteration is used for user names. Try :
Create a user : Beatrice
Try to change it to : Béatrice. Refused with message : User name already in use.
Try in two steps :

1. Change Beatrice to Béatrice1
2. Change Béatrice1 to Béatrice
   It works.

New test :

1. User Beatrice (without accent). Create a message with a link to Beatrice.
2. Change Beatrice to Béatrice : The previously created link continues to work, but you cannot create a new link to Béatrice. The working link is written :
   <a href="/d/7/43" class="PostMention" data-id="68">Beatrice</a>
   In the texte it appears like : Beatrice (without accent)

If you let the mouse on the link, you will see in the popup : "Béatrice : Blablabla..." with accent on Béatrice.

This mixing of two types of representation of the user (with or without accent) is the reason of the bug.

Solution : when creating a link to user, use the same type or transliteration which is used when creating the references to the posts.

[tobyzerner]

Thanks for the report. As discussed in #832 and #557, we've made a decision to disallow non-ASCII characters in usernames.