Display session expiry msg after auto-redirect.

Signed-off-by: Dhananjay Nakrani <dhananjaynakrani@gmail.com>

In the implementation of [feature-request#1460](http://sourceforge.net/p/phpmyadmin/feature-requests/1460/), there were some issues that I have tried to resolve.

1. After auto-redirection on session expiry, there was no msg shown to user. Now with these changes appropriate msg will be displayed on log-in form.
2. After re-login, user was taken to home page because `$GLOBALS['cfg']['PmaAbsoluteUri']` was used. Now user is taken to where he left off. This is similar to [feature-request#1426](http://sourceforge.net/p/phpmyadmin/feature-requests/1426/)
3. I've also renumbered the test cases in `testAuth()`.