Sticky encryption rule, requiring that all replies to encrypted messages
are encrypted, applies only to messages with a quote now.
Co-Authored-By: B. Petersen <r10s@b44t.com>
the footer mark normally used in email-conversations is `-- `,
note the trailing space, see RFC 3676, §4.3
unfortunately, the final space is removed by some providers,
which lead to footers showing up on delta-to-delta-conversations
(on nondc-to-delta, this is not an issue as we cannot be sure anyway
and show a [...] therefore)
this change accepts lines with only `--` as a footer separator
if there is no other footer separator
and if the line before is empty and the line after is not.
as there is still some chance to remove text accidentally,
see tests, some protection against that is needed in another commit.
