... and when it doesn't, it is not at all obvious how to configure Git to
use plink for SSH connections.
Well, it's basically mentioned in the release notes how to do that:
"You may also consider using PuTTY by pointing GIT_SSH to plink.exe and
handle your ssh keys with Pageant."
but the installer only checks for the presence of the PuTTY registry keys
below HKEY_CURRENT_USER; and since the installer runs as the admin user,
it doesn't find any saved sessions.
True, that's a draw-back of the current solution. But still I feel we're
getting less issue reports the way it works now that the way it worked
before. Before, we did exactly what you suggested, we looked for the PuTTY
executable in common places, and used that as a default location for plink.
It could also be the other way around, by the way: The admin has PuTTY
sessions, PuTTY is offered and the admin selects it. But if a user does not
want to use PuTTY for some reason, she would need to alter GIT_SSH /
SVN_SSH manually, too.
The simplest alternative would be to drop the check for saved sessions
entirely and go back to offering the choice of OpenSSH or plink directly
in the installer.