No check of too long MySQL users

[daniche]

In alternc database, MySQL users max length is 16 characters.

When creating a new dbuser through alternc where alterncUser_dbUser has more than 16 characters, there is a bug: AlternC shows a user named alterncUser_alterncUser, but no configuration or deletion is possible. You have to erase them in the alternc database.

A direct consequence is that an alternC user with a login longer than 15 characters, cannot create additional db users.

There should be some sanity check in the php scripts.

I don't know it the 16 char length is needed by MySQL, but if not, maybe better to modify the AlternC dbuser table.

[benjamin]

(In [2620]) Fixed #1174 : we check the length of mysql login everywhere. + english comments and misc code cleanup (hook functions at the end of the class)