Make botan’s policy configurable from a file

fix #3244

src/utils/dirname.cpp

@@ -0,0 +1,16 @@
+#include <utils/dirname.hpp>
+
+namespace utils
+{
+    std::string dirname(const std::string filename)
+    {
+      if (filename.empty())
+        return "./";
+      if (filename == ".." || filename == ".")
+        return filename;
+      auto pos = filename.rfind('/');
+      if (pos == std::string::npos)
+        return "./";
+      return filename.substr(0, pos + 1);
+    }
+}

src/utils/dirname.hpp

@@ -0,0 +1,6 @@
+#include <string>
+
+namespace utils
+{
+std::string dirname(const std::string filename);
+}

src/utils/xdg.hpp

@@ -10,5 +10,3 @@
  */
 std::string xdg_config_path(const std::string& filename);
 std::string xdg_data_path(const std::string& filename);
-
-