LDAP authentication username mismatch

[rhobincu]

When using LDAP to authenticate users, Web-CAT does not trim white spaces from the username during authentication. However the LDAP will authenticate the user regardless of the spaces at the beginning or end of the username. The end result is that Web-CAT will create multiple users (different for all intents and purposes) with different user IDs for the same username if the user will login by adding spaces at the start or end of the username which happens quite a lot when the student copy-paste their username.