zgrep(1): Note that -r/-R are not currently supported.

This is better behavior than just silently doing the wrong thing. We do not
currently have plans to support -r/-R with the compression-enabled greps.

Reported by:	jilles

usr.bin/grep/zgrep.sh

@@ -106,6 +106,10 @@ do
 	    silent=1
 	    shift
 	    ;;
+	-r|-R)
+	    echo "${prg}: the ${1} flag is not currently supported" >&2
+	    exit 1
+	    ;;
 	-V|--version)
 	    exec ${grep} -V
 	    ;;