sslutil: add a config knob to support TLS (default) or SSLv23 (bc) (
issue4038)
Prior to this change, we default to SSLv23, which is insecure because
it allows use of SSLv2. Unfortunately, there's no constant for OpenSSL
to let us use SSLv3 or TLS - we have to pick one or the other. We
expose a knob to revert to pre-TLS SSL for the user that has an
ancient server that lacks proper TLS support.
cmdutil.bailifchanged: standardize error message for dirty working dir
This affects rebase, graft, histedit, and other similar commands.