Fix race conditions in mod_disk_cache by properly using the tempfile rather

Fix race conditions in mod_disk_cache by properly using the tempfile rather
than the data file.  (We rename the tempfile when we're completed with the data
file which is an atomic operation.)

Part of the code assumed that it was using a temporary file; other parts
wrote directly to the body file - which was incorrect.  So, clean up the
whole mess to be consistent and more correct.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@105261 13f79535-47bb-0310-9956-ffa450edef68