Avoid a possible name clash in the temporary directory

Avoid a possible name clash in the temporary directory

As all the temporary files are generated in the same directory and some of
them may be named after the user's ID found in the log file, it is possible
that a user's file ends up with the same name as an internal file such as
the downloads.

To avoid that name clash, the temporary files created for any auxiliary
report are suffixed with a distinct extension.