I just ran into this while trying to build syslog-ng on a fresh unstable system. To avoid having to go an extra mile to fix my autobuilders, I plan to NMU json-c with the patch attached.
Unlike Steve's fix, this is merely a workaround, that adds the missing header to debian/libjson0-dev.install. This way, the extra build-dependency on dh-autoreconf is not needed, and if and when upstream integrates the fix, all that needs to be done is remove one line from the install file. To me, this sounds ligther, and as such, I will upload to DELAYED/0 in a few moments. -- |8]
diff -Nru json-c-0.10/debian/changelog json-c-0.10/debian/changelog --- json-c-0.10/debian/changelog 2012-08-17 18:57:36.000000000 +0200 +++ json-c-0.10/debian/changelog 2012-08-27 12:57:51.000000000 +0200 @@ -1,3 +1,11 @@ +json-c (0.10-1.1) unstable; urgency=low + + * Non-maintainer upload. + * Include the missing json_object_iterator.h header in + libjson0-dev. (Closes: #685714) + + -- Gergely Nagy <alger...@madhouse-project.org> Mon, 27 Aug 2012 12:56:32 +0200 + json-c (0.10-1) unstable; urgency=low * New upstream release (Closes: #684058) diff -Nru json-c-0.10/debian/libjson0-dev.install json-c-0.10/debian/libjson0-dev.install --- json-c-0.10/debian/libjson0-dev.install 2011-08-13 00:22:06.000000000 +0200 +++ json-c-0.10/debian/libjson0-dev.install 2012-08-27 12:51:28.000000000 +0200 @@ -3,3 +3,4 @@ usr/lib/*/libjson.so usr/include/* usr/lib/*/pkgconfig +json_object_iterator.h /usr/include/json/