* helm.el (helm-follow-mode): Issue #210 enable follow mode by source.
(helm-follow-execute-persistent-action-maybe): do it when follow attr exists.
* helm.el: Allow not allowing helm-follow-mode in some sources.

* helm-sys.el: do it in top.
* helm.el (helm-follow-mode): Use assq.
* helm-help.el: Document follow attribute.
* helm-pkg.el: Update version number.
* helm.el: Fix typo in docstring.
* helm.el (helm-follow-mode): Fix docstring.
* helm.el (helm-yank-selection): With a prefix arg use real value.
(helm-kill-selection-and-quit): Same.
* helm.el (helm-kill-selection-and-quit): Fix docstring.
* helm.el (helm-follow-mode): Limit follow-mode to current source, not all buffer.
(helm-follow-execute-persistent-action-maybe): Check only attr, not local var.
* helm.el (helm-follow-mode): Now a function.
(helm-find-files-down-one-level): Disable helm-follow-mode.
* helm.el (helm-follow-mode): Add now persistency; Issue #210.
(helm-follow-mode-persistent): New user var.
* helm.el: Fix now mode-line in follow-mode; Issue #210.
* helm-grep.el (helm-do-grep-1): Allow persistence in grep.
* helm.el (helm-follow-mode-persistent): Issue #210 default value is now nil.