Every client's reader thread (Telnet/RAW, serial, local shell, IRC, VNC,
RDP) and SSH's channel reader task now run under clients::guarded /
guarded_task. A panic there, such as a decoder bug triggered by a
hostile server, reports 'internal error: …' through the session's
on_error and then closes it, so the tab shows the error (and
auto-reconnect can run) instead of looking connected with nothing
reading. Other sessions were already unaffected since the switch to
parking_lot locks.
Andy Dixon
02bd237636