UPDATE: Build instructions (ZABW) for Windows

I have attached an updated ZABW build instructions for HEAD, from the
CVS /abi/docs/build/BUILD.zabw . I updated the Windows section to
comply with KJD's changes to the Windows build system, as well as fixing
one typo in that section. If somebody (probably Jeremy) could review,
export to TXT and HTML, and commit this, that would be good. (I could
not get a diff because it was in ZABW binary format)

Thanks!