Fix mlockall()/madvise() interaction.

mlockall(2) can cause purging via madvise(2) to fail.  Fix purging code
to check whether madvise() succeeded, and base zeroed page metadata on
the result.

Reported by Olivier Lecomte.

include/jemalloc/internal/chunk_mmap.h

@@ -9,7 +9,7 @@
 /******************************************************************************/
 #ifdef JEMALLOC_H_EXTERNS
 
-void	pages_purge(void *addr, size_t length);
+bool	pages_purge(void *addr, size_t length);
 
 void	*chunk_alloc_mmap(size_t size, size_t alignment, bool *zero);
 bool	chunk_dealloc_mmap(void *chunk, size_t size);

include/jemalloc/internal/extent.h

@@ -23,6 +23,9 @@ struct extent_node_s {
 
 	/* Total region size. */
 	size_t			size;
+
+	/* True if zero-filled; used by chunk recycling code. */
+	bool			zeroed;
 };
 typedef rb_tree(extent_node_t) extent_tree_t;