[web/staticcontrollers] create a unique temporary file for concat handling Predictable names means different processes can race against each other. Let's avoid that and use mkstemp to get a real unique temporary file, and atomically rename it when we're done. Closes #3524182

# -*- coding: utf-8 -*-
# copyright %(year)s %(author)s, all rights reserved.
# contact %(author-web-site)s -- mailto:%(author-email)s
#
%(long-license)s
"""%(distname)s specific hooks and operations"""