Language selector not respected on login screen page

[Robert Lyon]

We need to respect the language choice on the login screen

When you go to a page that can only be accessed when logged in it
takes you to the login screen (login box only screen).

When you have more than one language installed it displays a language
select form but if you pick a different language it reloads the page
again in the old language.

This patch allows it to remember what language was chosen and show the login box as the new language.

To replicate:

1. Install the Spanish language pack
2. Log out of Mahara
3. Go to /admin/
4. Because /admin/ is a non-public page, you will see the transient login screen
5. At the top of the transient login screen, you'll see the language-selection dropdown. Choose Spanish (Espanol) from the list and press the "Change" button

Expected result: The transient login screen reloads, in Spanish
Actual result: The transient login screen reloads, but the language is unchanged.

[Robert Lyon (robertl-9)]

Marked as low as most people could work out it is a login box without needing to have it translated.

The fix just removes the confusion of choosing a language and nothing changes

[Mahara Bot (dev-mahara)]

Patch for "master" branch: https://reviews.mahara.org/6638

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/6638
Committed: https://git.mahara.org/mahara/mahara/commit/61448e526f2e7e11121b1a63c7cdc8ef5e19b1b5
Submitter: Robert Lyon (<email address hidden>)
Branch: master

commit 61448e526f2e7e11121b1a63c7cdc8ef5e19b1b5
Author: Aaron Wells <email address hidden>
Date: Wed Jul 6 17:22:41 2016 +1200

Bug 1597957: Handle language select form on non-public pages

By moving the language select form's handler into
a Pieforms submit method, we ensure that the form
can be properly handled on any page that displays it.

behatnotneeded: Can't test multi-language with behat yet

Change-Id: I04aea40b9ba1000f75fc08ef7015fd00de3bc9da