IMplement the bugtracker #30935 that consists in computing the home page that is variable that was used without any assignment

The fix consists in a copy of the source code
It is inspired from the source present in Joomla 2.5.9
/module/mod_languages/helper.php line 23-29 that I copied as such in the plugin

To see the bug before, you need to use the language filter and run joomla in a debugger to see that $home is used without assignment.
The fix that can verified that the $home is correctly field.

This fix does not implement our remark concerning the fact that when a redirect page is present in the login, it is ignored.