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.

include/jemalloc/internal/jemalloc_internal.h.in

@@ -404,9 +404,8 @@ extern size_t const	index2size_tab[NSIZES];
 extern uint8_t const	size2index_tab[];
 
 arena_t	*a0get(void);
-void	*a0malloc(size_t size);
-void	*a0calloc(size_t num, size_t size);
-void	a0free(void *ptr);
+void	*a0malloc(size_t size, bool zero);
+void	a0dalloc(void *ptr);
 arena_t	*arenas_extend(unsigned ind);
 arena_t	*arena_init(unsigned ind);
 unsigned	narenas_total_get(void);

include/jemalloc/internal/private_symbols.txt

@@ -1,5 +1,4 @@
-a0calloc
-a0free
+a0dalloc
 a0get
 a0malloc
 arena_get
@@ -107,6 +106,9 @@ bitmap_set
 bitmap_sfu
 bitmap_size
 bitmap_unset
+bootstrap_calloc
+bootstrap_free
+bootstrap_malloc
 bt_init
 buferror
 chunk_alloc_arena

include/jemalloc/internal/tsd.h

@@ -48,7 +48,7 @@ typedef enum {
  *   void example_tsd_set(example_t *val) {...}
  *
  * Note that all of the functions deal in terms of (a_type *) rather than
- * (a_type)  so that it is possible to support non-pointer types (unlike
+ * (a_type) so that it is possible to support non-pointer types (unlike
  * pthreads TSD).  example_tsd_cleanup() is passed an (a_type *) pointer that is
  * cast to (void *).  This means that the cleanup function needs to cast the
  * function argument to (a_type *), then dereference the resulting pointer to