Nickname verifications on registration and updates for profiles (not yet
groups) have been improved.
Minor bugs in RegisterAction were also fixed, where multiple forms would
be outputed because the function did not return after showForm(). This
will be solved more permanently with throwing exceptions in the future.
This provides initial infrastructure for decoupling display names from internal canonical names, but continues to have us storing and using the canonical forms.
It should be/become possible to provide mixed-case and underscore-containing names in links, @-mention, !-group, etc, but we don't store those alternate forms generally.
