The WinSock library is now loaded at run-time, which means we can

attempt to load WS2 and then fall back to WS1 if that fails. This
should allow us to use WS2-specific functionality to find out the
local system's list of IP addresses, thus fixing winnet-if2lo, while
degrading gracefully back to the previous behaviour if that
functionality is unavailable. (I haven't yet actually done this; I've
just laid the groundwork.)
This checkin _may_ cause instability; it seemed fine to me on
initial testing, but it's a bit of an upheaval and I wouldn't like
to make bets on it just yet.

git-svn-id: svn://svn.tartarus.org/sgt/putty@3502 cda61777-01e9-0310-a592-d414129be87e