[web server] #1642893 issue a 403 instead of a 500 on Unauthorized exception
To do so, we allow an arbitrary code to be passed to ``error_handler``. Default
error code is still 500.
option_group_changed('port', 'main', 'web')
option_group_changed('query-log-file', 'main', 'web')
option_group_changed('profile', 'main', 'web')
option_group_changed('max-post-length', 'main', 'web')