Reenable helm-set-local-variable, fix it and use it where needed.
Merge branch 'master' into helm-local-var

Conflicts:
	helm.el
* helm.el (helm-set-local-variable): Add it again.
(helm): Append to local vars.
* helm-grep.el (helm-do-grep-1): Don't use not yet expanded value of local vars as value when setting locally.
* helm.el (helm): Local vars passed by keyword take precedence.
* helm.el (helm-set-local-variable): Fix docstring.