fs: fix --dump filters not always appearing

Before this fix, we initialised the options blocks in a random order.
This meant that there was a 50/50 chance whether --dump filters would
show the filters or not as it was depending on the "main" block having
being read first to set the Dump flags.

This initialises the options blocks in a defined order which is
alphabetically but with main first which fixes the problem.

fs/registry.go

@@ -531,7 +531,22 @@ func (oi *OptionsInfo) load() error {
 // their values read from the options, environment variables and
 // command line parameters.
 func GlobalOptionsInit() error {
-	for _, opt := range OptionsRegistry {
+	var keys []string
+	for key := range OptionsRegistry {
+		keys = append(keys, key)
+	}
+	sort.Slice(keys, func(i, j int) bool {
+		// Sort alphabetically, but with "main" first
+		if keys[i] == "main" {
+			return true
+		}
+		if keys[j] == "main" {
+			return false
+		}
+		return keys[i] < keys[j]
+	})
+	for _, key := range keys {
+		opt := OptionsRegistry[key]
 		err := opt.load()
 		if err != nil {
 			return err