Ensure LDAP provided email is always compared case-insensitively.

Created by: patthoyts

LDAP databases may store email addresses in mixed case so ensure we only work with a lower case version to avoid missing a valid account after LDAP login.

[PT: this commit resolves github issue #455 (closed)]

Signed-off-by: Pat Thoyts patthoyts@users.sourceforge.net