Modifications to make mod_unique_id thread safe. This should work on Windows,

but no guarantees.  I haven't verified it will always give a unique ID, but
the logic is good.  I'll write some test cases to see if I can make it fail
later.

Submitted by:	Ryan Bloom


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@83789 13f79535-47bb-0310-9956-ffa450edef68