Add an explicit --disable-avahi to the configuration options.

Previous defaults remain --- the option must be explicitly
defined to be used. Thanks to E. Liddell.

configure.in.in

@@ -98,7 +98,7 @@ KDE_CHECK_LIB(gmp, __gmpz_init,	[have_gmp=yes],
 		AC_MSG_ERROR(libgmp is required to install this program)
 	])
 
-KDE_CHECK_HEADER(gmp.h, [have_gmp=yes], 
+KDE_CHECK_HEADER(gmp.h, [have_gmp=yes],
 	[
 		have_gmp=no
 		AC_MSG_ERROR(libgmp is required to install this program)
@@ -198,26 +198,31 @@ fi
 m4_pattern_allow(PKG_CONFIG_MIN_VERSION)
 PKG_PROG_PKG_CONFIG
 
-PKG_CHECK_MODULES( AVAHI,  avahi-client >= 0.6.10, 
-[ 
-	AC_SUBST(AVAHI_CFLAGS)
-	AC_SUBST(AVAHI_LIBS)
-	avahi=true
-],
-[
-	missing_avahi_warning=yes
-	avahi=false
-])
-
-PKG_CHECK_MODULES( AVAHI_TQT,  avahi-tqt >= 0.6.10, 
-[ 
-	AC_SUBST(AVAHI_TQT_CFLAGS)
-	AC_SUBST(AVAHI_TQT_LIBS)
-	avahi=true
-],
-[
-	missing_avahi_warning=yes
-	avahi=false
-])
+AC_ARG_WITH([avahi], AS_HELP_STRING([--without-avahi], [Build without avahi/ZeroConf support (default: test)]))
+
+avahi=false
+if test "x$with_avahi" != "xno"; then
+ PKG_CHECK_MODULES( AVAHI,  avahi-client >= 0.6.10,
+ [
+   AC_SUBST(AVAHI_CFLAGS)
+   AC_SUBST(AVAHI_LIBS)
+   avahi=true
+ ],
+ [
+   missing_avahi_warning=yes
+   avahi=false
+ ])
+
+ PKG_CHECK_MODULES( AVAHI_TQT,  avahi-tqt >= 0.6.10,
+ [
+   AC_SUBST(AVAHI_TQT_CFLAGS)
+   AC_SUBST(AVAHI_TQT_LIBS)
+   avahi=true
+ ],
+ [
+   missing_avahi_warning=yes
+   avahi=false
+ ])
+fi
 
 AM_CONDITIONAL(COMPILE_ZEROCONF, test x$avahi = xtrue)