This is the pathfinding change that proves it's possible for _one_
Conf setting to become Unicode-capable.
That seems like quite a small reward for all the refactoring in the
previous patches this week! But changing over one configuration
setting is enough to get started with: once all the bugs are out of
this one, we can try switching over some more.
Changing the type to CONF_TYPE_STR_AMBI is enough by itself to make
the configuration dialog box write it into Conf as UTF-8, because
conf_editbox_handler automatically checks whether that possibility is
available. However, setting the same Conf entry from the command line
isn't automatic: I had to add code in the handler for the -l
command-line option in cmdline.c.
This commit also doesn't yet handle the _other_ way to specify a
username on the command line: including it as part of the hostname
argument via "putty user@host" or similar. That's more difficult,
because it also requires deciding what to do about UTF-8 in the actual
hostname.
(That looks as if it ought to be possible: Windows should be able to
handle looking up Unicode hostnames if you use GetAddrInfoW() in place
of getaddrinfo(). But plumbing it through everything in between
cmdline.c and windows/network.c is a bigger job than I'm prepared to
do in this proof-of-concept commit.)
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