* helm.el (helm--set-local-variable): New.
* helm.el (helm--let-internal, helm--let-variables): Renamed from helm-let-internal and helm--let-variables.
* helm.el (helm--set-local-variable): Allow binding after init.
* helm.el (helm--local-variables): new.
(helm-set-local-variable): use it.
(helm-create-helm-buffer): append helm--local-variables to helm--let-variables.