(bug 49003) Fixed password change for lowercase username

Mediawiki munges the username. When using lowercase usernames the
username provided should be converted back to lowercase before
comparing it with the username retrieved from LDAP or else it will
always fail.

Change-Id: Ic034502d2a87c32541872d01b7d7b5e9ccb2e101
Merge "(bug 49003) Fixed password change for lowercase username"