Deglobalise the Unicode module. Despite all my grand plans, I've

just done this the very simple way - bundle all the globals into a
data structure and pass pointers around. One particularly ugly wart
is that wc_to_mb now takes a pointer to this structure as an
argument (optional, may be NULL, and unused in any Unicode layer
that's even marginally less of a mess than the Windows one). I do
need to do this properly at some point, but for now this should just
about be adequate. As usual, the Mac port has not been updated.

git-svn-id: svn://svn.tartarus.org/sgt/putty@2592 cda61777-01e9-0310-a592-d414129be87e