* helm.el (helm--in-update): New flag.
(helm-check-minibuffer-input): set it before running update.
Reset it in helm-after-update-hook.
(helm--updating-p): Use it.
* helm.el (helm-exit-idle-delay): New user var.
(helm--reset-update-flag): New run in helm-after-update-hook.
Reset helm--in-update after helm-exit-idle-delay seconds.
* helm.el (helm--updating-p): Add comments no--code-change.