[trac812] made sure libutil_io is linked from dns/tests as agreed in review.

src/lib/dns/tests/Makefile.am

@@ -57,6 +57,7 @@ run_unittests_LDADD = $(GTEST_LDADD)
 run_unittests_LDADD += $(top_builddir)/src/lib/dns/libdns++.la
 run_unittests_LDADD += $(top_builddir)/src/lib/util/libutil.la
 run_unittests_LDADD += $(top_builddir)/src/lib/util/unittests/libutil_unittests.la
+run_unittests_LDADD += $(top_builddir)/src/lib/util/io/libutil_io.la
 run_unittests_LDADD += $(top_builddir)/src/lib/exceptions/libexceptions.la
 endif