Fix tsd cleanup regressions.

Fix tsd cleanup regressions that were introduced in
5460aa6f66 (Convert all tsd variables to
reside in a single tsd structure.).  These regressions were twofold:

1) tsd_tryget() should never (and need never) return NULL.  Rename it to
   tsd_fetch() and simplify all callers.
2) tsd_*_set() must only be called when tsd is in the nominal state,
   because cleanup happens during the nominal-->purgatory transition,
   and re-initialization must not happen while in the purgatory state.
   Add tsd_nominal() and use it as needed.  Note that tsd_*{p,}_get()
   can still be used as long as no re-initialization that would require
   cleanup occurs.  This means that e.g. the thread_allocated counter
   can be updated unconditionally.

include/jemalloc/internal/quarantine.h

@@ -49,8 +49,8 @@ quarantine_alloc_hook(void)
 
 	assert(config_fill && opt_quarantine);
 
-	tsd = tsd_tryget();
-	if (tsd != NULL && tsd_quarantine_get(tsd) == NULL)
+	tsd = tsd_fetch();
+	if (tsd_quarantine_get(tsd) == NULL && tsd_nominal(tsd))
 		tsd_quarantine_set(tsd, quarantine_init(tsd, LG_MAXOBJS_INIT));
 }
 #endif