Previously Delta Chat tried all DNS resolution results
in sequence until TCP connection is established successfully,
then tried to establish TLS on top of the TCP connection.
If establishing TLS fails, the whole
connection establishment procedure failed
without trying next DNS resolution results.
In particular, in a scenario
where DNS returns incorrect result
pointing e.g. to a server
that listens on the TCP port
but does not have correpsponding TLS certificate,
Delta Chat now will fall back to the cached result
and connect successfully.
we're always checking the configuration encrypted.
saying it is 'preferred' encrypted is misleading,
therfore, just remove it.
i do not think, it is worth saying that we do not query 'http',
this is clear from the source code.
moreover, fix two typos.
This certificate does not exist on older Android phones.
It is already added manually for IMAP and SMTP,
this commit adds the same certificate for HTTP requests.
async-smtp does not implement read buffering anymore
and expects library user to implement it.
To implement read buffer, we wrap streams into BufStream
instead of BufWriter.
