Add a tool for removing stale *.pyc files

(imported from commit c0fcfb171932f523fff13f14f09ecf5b3a6b21de)

tools/clean-repo

@@ -0,0 +1,11 @@
+#!/bin/bash -e
+
+# Remove .pyc files to prevent loading stale code.
+#
+# You can run it automatically on checkout:
+#
+#     echo ./tools/clean-repo > .git/hooks/post-checkout
+#     chmod +x .git/hooks/post-checkout
+
+cd "$(dirname "$0")/.."
+find . -name '*.pyc' -print -delete | sed 's|^|[clean-repo] Deleting |'