[BUG] org-agenda-filter and hyphens in category names

[Matt Lundin]

Hi everyone,

I'm just getting around to exploring the function org-agenda-filter
introduced last year. (Due to busyness, I was running an older version
of Org Mode last year for fear of breaking features I relied on.)

I like the tab completion. However, I'm finding that the completion for
categories often fails because of hyphens in my file and category names.
Let's say I have a file named "my-file.org" with active todos. The
function org-agenda-filter will suggest "my-file" as a possible category
completion. However, if I tab complete "my-file," org-agenda-filter
errors out with the following messages:

  ‘+my’ filter ignored because tag/category is not represented
  ‘-file’ filter ignored because tag/category is not represented

The same thing occurs when I put hyphens in filetags.

Looking at the Org Manual, I see that Org Mode restricts tags to
alphanumeric characters, "@", and "_". And org-set-tags-command will
sanitize tag names when entering them, replacing forbidden characters
with ":".

However, there are no guidelines about forbidden characters in
categories. And filetags at the top of file allow for arbitrary
characters. Both org-agenda-filter-by-category ("<") and
org-agenda-filter-by-tag ("\") work with categories and filetags
containing "-" or "+" in the name.

Would it be possible for org-agenda-filter to escape the set of special
characters [-+<>=/] in category and filetag names when offering them for
completion? 

Best,

Matt