#275 fingerprint warning when switching syncterm versions

[Andy Alt]

When I test syncterm using the latest git build and connect to a BBS I
previously connected to with ssh in syncterm 1.8, I get a message that the
fingerprint has changed (disconnect, update, ignore) . The message doesn't appear when i switch back to 1.8.
Is that somehow expected behavior? The host key hasn't actually changed, so is
syncterm reading it differently? The way I understand the normal operation of ssh is that the host key never changes, and upon connecting to a host the first time, the host key is stored so it can be matched each time. If there's a mismatch, the connection fails and can't be bypassed unless a cli switch is used or the original host key is deleted from ~/.ssh/known_hosts. But I'm not familiar yet with how syncterm handles things...

[Stephen James Hurd]

SyncTERM < 1.10 stored an incorrect fingerprint... it was effectively an MD5 in a SHA-1 sized value. I expect SyncTERM to autodetect this and silently update it when 1.10a is being ran. However, once 1.10a updates it, it won't match on older versions, which should be the ones indicating a mismatch (since they don't properly support the updated fingerprint).

Switching back and forth between versions is not supported, and may result in various odd effects. Only moving from older to newer versions is supported.