PATCH: Cygwin: file mode support and ufs writecleanswap bugfix

Hi,
If one of the core team could look over this patch and if acceptable drop into HEAD & squid 2.4 sometime soon I'd really appreciate
it.

It's all cleanly #if defined, except for one little bit in store_dir_ufs.c, where I've solved a somewhat general case (that would
only affect platforms which don't let you rename open files - OS/2/Cygwin/NT).

This should all go into squid 2.4 & head. Without it users on cygwin with text mode mounts will die badly, and all cygwin users will
not ever see a (CLEAN) status on their cache_dir's. Why I was getting clean status when I first looked into this may be due to some
of the 'emulation' work done on cygwin to make UN*X assumptions (ie unlinking open files) work somewhat.

As a side note, I've reactivated the cygwin branch, (where this work currently resides), and I will be doing some experimental stuff
there in the near future: so use the attached patch, not a CVS diff.

Thanks,
Rob