It can't be obsoleted because that causes builds with an old
${DESTDIR}/usr/include/kerberosIV/des.h to fail in directories which
have CPPFLAGS+=-I${DESTDIR}/usr/include/kerberosIV so that their #include
of <krb.h> works (and any subsequent #include <foo.h> by <krb.h>).
(Note: gcc3 won't work with a hack such as prepending -I${DESTDIR}/usr/include
before -I${DESTDIR}/usr/include/kerberosIV.)
Affected directories include lib/libkafs, and any thirdparty source
which used a similar -I/usr/include/kerberosIV hack to use <krb.h>.
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