#8266 LDAP preferences provider issues
Document user_prefs_storage.ldap.fields.* better. display_name is required, and email_address would be good. Give fuller examples of what they mean.
allura.model.auth.User#register calls set_pref but LDAP could be configured in a readonly manner. So then registration errors. LDAP prefs provider should fail gracefully, or maybe skip updates entirely if allow_edit_prefs is false.