Steal a play from mod_proxy, which taught us this Win32 lesson. Threaded

  Steal a play from mod_proxy, which taught us this Win32 lesson.  Threaded
  local storage must be allocated with the Tls*() family of functions, or
  the dynamically loaded module _will_ clobber our clib's (msvcrt's) own
  thread saftey stacks.

  I _don't_ know what the other multithread platforms require in terms of
  initialization.  OS2/Netware maintainers can steal the idea from the
  Win32 get_cur_unique_id() implementation, to initialize other copies
  on the fly (if required.)  They may already call child_init for every
  thread, so child_init could call the master_init to set up this thread's
  variables.  Remember that the get_cur_unique_id() applies to straight
  un*x fork implementations as well, so protect with #ifdef PLAT sections.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@91233 13f79535-47bb-0310-9956-ffa450edef68