PATCH: os2 support for ufs & cygwin bugfix

Hi,
the attached patch allows OS2 to compile the ufs fs module, and fixes a
problem with cygwin. I think it should go into 2.4 as well as HEAD (pending
acceptance of course).

Does anyone know _why_ the new swapstate file is unlinked _after_ it is
opened? Cygwin can't unlink an open file, so it queues the unlink and
executes it as soon as the file is closed. Which happens right before we
rename it - because the windows platform cannot rename in use files.

I haven't looked at diskd or aufs to see if they have this issue as well...
and I dont' know why I missed it in my original cygwin work :-[

Rob