request #6154 - Cannot change password upon expiration

Behaviour change:
- Before this commit, user was not authenticated (session/Cookie) when they
  were changing their password
- Now, the session is open but we ensure that they don't access something else
  than the password change page (change_pw) until they actually change the F%*!
  password.

Security plus:
* The password changing form is CSRF checked
* The login screen is brute force protected (it was not the case of change_pw)

Change-Id: I3d553633b53d46d906c322dfe2e912129df2a9d5
Merge commit 'refs/changes/59/1859/5' of http://gerrit.tuleap.net/tuleap into HEAD

* http://gerrit.tuleap.net/tuleap:
  request #6154 - Cannot change password upon expiration

Change-Id: I72a3322684cbb578b2d0d5ebfb7a1e217d7a1db3
This is Tuleap 6.10.99.21

Change-Id: Ie2c95b3c5173810fbf7394b4f2d68e635af1c52a