Use helm-maybe-exit-minibuffer where needed, update autoloads.

* helm-config.el: Update autoloads.
* helm-help.el:    use helm-maybe-exit-minibuffer where needed.
* helm-imenu.el:   use helm-maybe-exit-minibuffer where needed.
* helm-mode.el:    use helm-maybe-exit-minibuffer where needed.
* helm-semantic.el:use helm-maybe-exit-minibuffer where needed.
* helm-utils.el:   use helm-maybe-exit-minibuffer where needed.
* helm.el:         use helm-maybe-exit-minibuffer where needed.
* helm-files.el (helm-find-files-get-candidates): change var name, fix comment.
* helm-files.el (helm-find-file-or-marked): Set `helm-ff-default-directory' and push it to history when creating new dir.
(helm-find-files-get-candidates): Fix comments.