Move dependencies in 'external' directory and pdate git submodules

external/Catch2/tools/scripts/checkDuplicateFilenames.py

@@ -0,0 +1,14 @@
+#!/usr/bin/env python3
+
+import os
+import sys
+
+files_set = set()
+
+for root, dir, files in os.walk("src/catch2"):
+    for file in files:
+        if file not in files_set:
+            files_set.add(file)
+        else:
+            print("File %s is duplicate" % file)
+            sys.exit(1)