PSFTP was ignoring `-1' and `-2' and always using SSH-2 with fallback to

PSFTP was ignoring `-1' and `-2' and always using SSH-2 with fallback to
SSH-1. It also ignored any settings forbidding fallback to SSH-1.

Ignoring `-1' and `-2' is hardly the end of the world, as it'd be difficult
to think of a realistic situation where fallback didn't do the right thing
and PSFTP was still useful. However, ignoring a user's `SSH-2 only' setting
was a bit rude.

git-svn-id: svn://svn.tartarus.org/sgt/putty@4357 cda61777-01e9-0310-a592-d414129be87e