Always compile test failure issue 1000000

Add more error checking in key parsing

Shrink unknown key tag parsing, similar to what happened in unknown sig tag

Rework the entire mheader file - Rename mheader to ltok (lexical token) - Make all skip functions const - Add a few missing functions

Make sure we don't crash on invalid headers

Always move to dkim_message_verify from dkim_rr_resolve to avoid hangs

t tag must be smaller than x tag

Make sure that l-tag is smaller than body

Check that i-tag is (sub)domain of d-tag

return early if there are missing tags in DKIM-Signature

Don't forget to reset bctx in between calls

Fix some inverted logic in the key's s-tag

Fix pointer forward movement for simple case of fws range

Fix key h tag: - inverted logic for key-h-tag-value - restore temporary NUL-character

Initial implementation for filter-dkimverify. Probably still contains quite a few bugs and does't yet support ed25519.