fst: hide sockets exposed via Filesystem

This is mostly useful for permissive defaults.

Signed-off-by: Ophestra <cat@gensokyo.uk>

fst/path.go

@@ -0,0 +1,11 @@
+package fst
+
+import (
+	"path/filepath"
+	"strings"
+)
+
+func deepContainsH(basepath, targpath string) (bool, error) {
+	rel, err := filepath.Rel(basepath, targpath)
+	return err == nil && rel != ".." && !strings.HasPrefix(rel, string([]byte{'.', '.', filepath.Separator})), err
+}