cleanup patches for 0.25

[David Bremner]

[PATCH 1/4] util: make g_mime_utils_header_decode_date_unix match
This I already pushed, as it seemed a bit urgent

[PATCH 3/4] emacs: convert remaining format-versions from 3 to 4

I don't really know why this wasn't done in the first place, but since the update from 3 to 4 is hassle free on the emacs side, may as well be consistent

[PATCH 4/4] debian: allow emacs25 as a build depends

Another thing I've been meaning to fix, now seems like a good time.