Fixes to the "reset password" mode of Special:ChangeEmail

Fixes to the "reset password" mode of Special:ChangeEmail

- Use the current User object when the user modifies its own password instead of different object (so that the fields are correctly updated on that object)
- Only set the cookies when changing the password of the current user and not when resetting the user's password. This was hiding the problem below.
- Make the internal call to Special:UserLogin call from Special:ChangeEmail actually work.
  The problem is that the $this->mNewPass field is cleared by attemptReset(). This was hidden because of the above and because the user is always redirected.
- Do not show the form and the message after successful submission (this was hidden for the same reason as above).
- Let Special:UserLogin handle the redirect itself when calling (because it might want to show something, such as what is injected by the UserLoginComplete hook)

Change-Id: I6cf15e23c905dad9612bab76a2dae5eb613fea9b