Audit tr(1)

A tool of my own devising, except from a small style-fix this code
has already been triple-checked.

README

@@ -77,7 +77,7 @@ The following tools are implemented ('*' == finished, '#' == UTF-8 support,
 =*| test            yes                          none
 =*| time            yes                          none
 =*| touch           yes                          none
-#*  tr              yes                          none
+#*| tr              yes                          none
 =*| true            yes                          none
 =*| tty             yes                          none
 =*| uname           yes                          none

tr.c

@@ -192,7 +192,7 @@ main(int argc, char *argv[])
 		usage();
 	} ARGEND;
 
-	if (argc < 1 || argc > 2 || (argc == 1 && dflag == sflag))
+	if (!argc || argc > 2 || (argc == 1 && dflag == sflag))
 		usage();
 	set1ranges = makeset(argv[0], &set1, &set1check);
 	if (argc == 2)