main: provide just binary name in help output

Otherwise it prints out complete path which is probably not desired and
we would need to filter out paths in the test's output etc.

Signed-off-by: Petr Štetiar <ynezz@true.cz>

main.c

@@ -36,7 +36,7 @@
 
 
 static void
-print_usage(char *app)
+print_usage(const char *app)
 {
 	printf(
 	"== Usage ==\n\n"
@@ -51,7 +51,7 @@ print_usage(char *app)
 	"  -e Set global variables from given JSON object\n"
 	"  -E Set global variables from given JSON file\n"
 	"  -m Preload given module\n",
-		app);
+		basename(app));
 }
 
 static void