add checkpoint.c and .h

src/checkpoint.h

@@ -0,0 +1,16 @@
+#ifndef _CHECKPOINT_H_
+#define _CHECKPOINT_H_
+
+#include <pool.h>
+
+/* checkpoint_save() stores states to a checkponint file (pathname) */
+int checkpoint_save(const char *pathname, int dir, char *remote_host, pool *path_pool,
+		    pool *chunk_pool);
+
+/* checkpoint_load() reads a checkpoint file (pathname). If path_pool
+ * and chunk_pool are NULL, This function fills only *remote and *dir.
+ */
+int checkpoint_load(const char *pathname, char *remote, size_t len, int *dir,
+		    pool *path_pool, pool *chunk_pool);
+
+#endif /* _CHECKPOINT_H_ */