[krbdev.mit.edu #2628] Patch to build krb5-1.3.4 under Cygwin

[Ken Raeburn via RT]

The suggested conditionalizing of DNS functions has already been done. 
The other patches were reasonable general cleanup and have been
installed.  I can't currently test a build on cygwin, but (1) cygwin is
low priority for MIT, and (2) this report is kind of old and based on
old sources.  So I'm closing it out with these fixes installed; if there
are still cygwin build problems, we can handle them in a new ticket.