This continues the programme of UTF-8 support in authentication, begun
in commit f4519b6533 which arranged for console userpass prompts
to function in UTF-8 when the prompts_t asked them to. Since the new
line editing setup works properly when it _is_ in UTF-8 mode, I can
now also arrange that it puts the terminal into UTF-8 mode in the
right circumstances.
I've extended the applicability of the '-legacy-charset-handling' flag
introduced by the commit mentioned above, so that now it's not
specific to the console front end. Now you can give it to GUI PuTTY as
well, which restores the previous (wrong) behaviour of accepting
username and password prompt input in the main session's configured
character set. So if this change breaks someone's workflow, they
should be able to have it back.
f9943e2ffd