Refactor bootstrapping to delay tsd initialization.

Refactor bootstrapping to delay tsd initialization, primarily to support
integration with FreeBSD's libc.

Refactor a0*() for internal-only use, and add the
bootstrap_{malloc,calloc,free}() API for use by FreeBSD's libc.  This
separation limits use of the a0*() functions to metadata allocation,
which doesn't require malloc/calloc/free API compatibility.

This resolves #170.

src/tsd.c

@@ -15,14 +15,14 @@ void *
 malloc_tsd_malloc(size_t size)
 {
 
-	return (a0malloc(CACHELINE_CEILING(size)));
+	return (a0malloc(CACHELINE_CEILING(size), false));
 }
 
 void
 malloc_tsd_dalloc(void *wrapper)
 {
 
-	a0free(wrapper);
+	a0dalloc(wrapper);
 }
 
 void