[O] Sticky agenda branch merged

[Max Mikhanosha]

I had just pushed a merge of max-sticky-agenda branch to master, let
me know if there are any problems, also feel free to hack/iterate on
it, if you have question as to why something was done, I'll do my best
to answer.

In particular I just seen a new commit introducing filter on
categories, and org-agenda-filtered-by-top-category probably needs to
be included into local variable list to have it work per agenda
buffer.

Also the individual calls to org-todo-list and such, do not work right
with sticky agenda as there is nothing to catch the 'exit tag, that is
thrown by `org-prepare-agenda' when it finds cached buffer. I'm not
sure there is more elegant way of fixing it, other then wrapping all
the individual scanner pieces with (catch) blocks, that re-throw if
they had detected that they been called from (org-agenda) command

Regards,
  Max