Not having zlib-dev installed causes gst-plugins-ugly to bail out while compiling:

make[3]: Entering directory `/root/gst-cvs/gst-plugins-ugly/gst/realmedia'
if /bin/sh ../../libtool --tag=CC --mode=compile gcc -DHAVE_CONFIG_H -I. -I. -I../..    -I../../gst-libs -I../../gst-libs -pthread -I/usr/local/include/gstreamer-0.10 -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/libxml2   -Wall -Werror  -g   -DGST_DISABLE_DEPRECATED -pthread -I/usr/local/include/gstreamer-0.10 -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/libxml2   -g -O2 -MT libgstrmdemux_la-rmdemux.lo -MD -MP -MF ".deps/libgstrmdemux_la-rmdemux.Tpo" -c -o libgstrmdemux_la-rmdemux.lo `test -f 'rmdemux.c' || echo './'`rmdemux.c; \
        then mv -f ".deps/libgstrmdemux_la-rmdemux.Tpo" ".deps/libgstrmdemux_la-rmdemux.Plo"; else rm -f ".deps/libgstrmdemux_la-rmdemux.Tpo"; exit 1; fi
 gcc -DHAVE_CONFIG_H -I. -I. -I../.. -I../../gst-libs -I../../gst-libs -pthread -I/usr/local/include/gstreamer-0.10 -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/libxml2 -Wall -Werror -g -DGST_DISABLE_DEPRECATED -pthread -I/usr/local/include/gstreamer-0.10 -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/libxml2 -g -O2 -MT libgstrmdemux_la-rmdemux.lo -MD -MP -MF .deps/libgstrmdemux_la-rmdemux.Tpo -c rmdemux.c  -fPIC -DPIC -o .libs/libgstrmdemux_la-rmdemux.o
rmdemux.c:37:18: error: zlib.h: No such file or directory
make[3]: *** [libgstrmdemux_la-rmdemux.lo] Error 1
make[3]: Leaving directory `/root/gst-cvs/gst-plugins-ugly/gst/realmedia'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/root/gst-cvs/gst-plugins-ugly/gst'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/root/gst-cvs/gst-plugins-ugly'
make: *** [all] Error 2

Instead, a configure error should be printed or realmedia should just not be compiled.

(Installig libz-dev fixes the problem.)