* nnmairix.el: Remove old documentation in the commentary block.

* nnmairix.el: Remove old documentation in the commentary block.
(nnmairix-request-group): Do not update active file for nnml back ends.
(nnmairix-retrieve-headers): Set gnus-nov-is-evil to t for nnimap back
end so that overview files are ignored.
(nnmairix-update-groups): Make updating the groups more robust by using
marks.
(nnmairix-determine-original-group-from-path): Circumvent mairix bug
with dollar characters in message-id.