ASN1Message(True) may go off parsing arbitrary input data as
"something ASN.1" This could be GBs of octet strings or just very
long sequences. Avoid this by open-coding some top-level types expected.
This also tries to avoid some of the &parse-from usages that result
in unnecessary copies of data.
Adds a locally generated PCAP with addRequest/addResponse that we
don't currently handle.
