Move thread bindings to (ice-9 threads)

* libguile/init.c (scm_i_init_guile): Don't call scm_init_thread_procs.
* libguile/threads.c (scm_init_ice_9_threads): Rename from
  scm_init_thread_procs, make static.
  (scm_init_threads): Register scm_init_thread_procs extension.
* libguile/threads.h (scm_init_thread_procs): Remove decl.
* module/ice-9/boot-9.scm: Load (ice-9 threads), so that related side
  effects occur early.
* module/ice-9/deprecated.scm (define-deprecated): Fix to allow
  deprecated bindings to appear in operator position.  Export deprecated
  bindings.
  (define-deprecated/threads, define-deprecated/threads*): Trampoline
  thread bindings to (ice-9 threads).
* module/ice-9/futures.scm: Use ice-9 threads.
* module/ice-9/threads.scm: Load scm_init_ice_9_threads extension.
  Reorder definitions and imports so that the module circularity
  with (ice-9 futures) continues to work.
* module/language/cps/intmap.scm:
* module/language/cps/intset.scm:
* module/language/tree-il/primitives.scm: Use (ice-9 threads).
* module/language/cps/reify-primitives.scm: Reify current-thread
  in (ice-9 threads) module.
* module/srfi/srfi-18.scm: Use ice-9 threads with a module prefix, and
  adapt all users.  Use proper keywords in module definition form.
* test-suite/tests/filesys.test (test-suite):
* test-suite/tests/fluids.test (test-suite):
* test-suite/tests/srfi-18.test: Use ice-9 threads.
* NEWS: Add entry.
* doc/ref/api-scheduling.texi (Threads): Update.
* doc/ref/posix.texi (Processes): Move current-processor-count and
  total-processor-count docs to Threads.

libguile/init.c

@@ -415,7 +415,6 @@ scm_i_init_guile (void *base)
   scm_init_root ();		  /* requires continuations */
   scm_init_threads ();            /* requires smob_prehistory */
   scm_init_gsubr ();
-  scm_init_thread_procs ();       /* requires gsubrs */
   scm_init_procprop ();
   scm_init_alist ();
   scm_init_async ();              /* requires smob_prehistory */