Yet more global-removal. The static variables in logging.c are now

absent, and also (I think) all the frontend request functions (such
as request_resize) take a context pointer, so that multiple windows
can be handled sensibly. I wouldn't swear to this, but I _think_
that only leaves the Unicode stuff as the last stubborn holdout.

git-svn-id: svn://svn.tartarus.org/sgt/putty@2147 cda61777-01e9-0310-a592-d414129be87e