Logging in to codereview.qt.nokia.com can easily create near-duplicate accounts by using mixed case in username

The linking between codereview.qt.nokia.com and bugreports.qt.nokia.com accounts is broken in such a way that duplicate accounts can be easily created by accident.

If bugreports user jane_doe logs in to gerrit, with username "jane_doe", then later logs in again with username "Jane_Doe", gerrit will silently create a new user account. "jane_doe" and "Jane_Doe" will be linked to the same bugreports account, but they will have separate identities, watch lists etc.