Only run swapon/swapoff if they exist

To silence warnings at startup/shutdown, check for existance of swapon
and swapoff before calling them.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/finit.c

@@ -333,7 +333,8 @@ static void fs_mount_all(void)
 	_d("Calling extra mount hook, after mount -a ...");
 	plugin_run_hooks(HOOK_MOUNT_POST);
 
-	run("swapon -ea", "swapon");
+	if (whichp("swapon"))
+		run("swapon -ea", "swapon");
 
 	_d("Finalize, ensure common file systems are available ...");
 	fs_finalize();

src/sig.c

@@ -321,7 +321,8 @@ void do_shutdown(shutop_t op)
 
 	/* Unmount any tmpfs before unmounting swap ... */
 	unmount_tmpfs();
-	run("swapoff -e -a", "swapoff");
+	if (whichp("swapoff"))
+		run("swapoff -e -a", "swapoff");
 
 	/* ... unmount remaining regular file systems. */
 	unmount_regular();