[O] Agenda: Don't widen narrowed subtrees

[Moritz Ulrich]

When a file used in the org-agenda is in a narrowed state
(org-narrow-to-subtree or similar) and you refresh the agenda buffer
via `g', it becomes un-narrowed. This is a very annoying behavior as I
tend to narrow to subtrees while editing their contents.

Is this a bug or desired behavior? If the latter, I'll try hunting the
missing `save-restriction' down tomorrow.

-- 
Moritz Ulrich