Add mq (message queue) to test infrastructure.

Add mtx (mutex) to test infrastructure, in order to avoid bootstrapping
complications that would result from directly using malloc_mutex.

Rename test infrastructure's thread abstraction from je_thread to thd.

Fix some header ordering issues.

include/jemalloc/internal/jemalloc_internal_defs.h.in

@@ -1,3 +1,5 @@
+#ifndef JEMALLOC_INTERNAL_DEFS_H_
+#define	JEMALLOC_INTERNAL_DEFS_H_
 /*
  * If JEMALLOC_PREFIX is defined via --with-jemalloc-prefix, it will cause all
  * public APIs to be prefixed.  This makes it possible, with some care, to use
@@ -193,3 +195,5 @@
 
 /* sizeof(intmax_t) == 2^LG_SIZEOF_INTMAX_T. */
 #undef LG_SIZEOF_INTMAX_T
+
+#endif /* JEMALLOC_INTERNAL_DEFS_H_ */