win32 use hashtable for fd management

win32 use hashtable for fd management

At least some win32 uses an opaque pointer for fd that is not
an ordinal like it is in unix.

Resurrect the old hashtable management for that platform to use
instead, and introduce a helper to get the wsi from the fd "somehow".

Signed-off-by: Bud Davis <bdavis9659@gmail.com>