MT#10837 Adjust FREERADIUS behaviour

'dpkg --list libfreeradius-client-dev' returns with exit code 0 if the
cowbuilder environment knows about the libfreeradius-client-dev
package, even if it's not installed at the time of execution.

A cleaner solution would be to handle this through autoconf & family,
but as that's not available in upstream sources let's fall back to a
simple check for presence of file /usr/include/freeradius-client.h.

Change-Id: I53c727be29ff2639f304a4ce009267b9e125c70e

debian/rules

@@ -23,7 +23,7 @@ include /usr/share/dpkg/buildflags.mk
 export JAVA_HOME=/usr/lib/jvm/java-gcj
 
 # choose radius lib
-export FREERADIUS=$(shell dpkg --list libfreeradius-client-dev >/dev/null 2>&1 && echo 1 || echo 0)
+export FREERADIUS=$(shell test -f /usr/include/freeradius-client.h && echo 1 || echo 0)
 
 # modules not in the "main" kamailio package
 EXCLUDED_MODULES=