write_shared_index(): use tempfile module

diff --git a/RelNotes b/RelNotes
index bcb4fb98ff925389797125283e40c6e397efc1fd..3295d667f396a686891335ceaaf817545a7d9e25 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/1.7.11.txt
\ No newline at end of file
+Documentation/RelNotes/2.5.0.txt
\ No newline at end of file