add disk.h and disk.c

Makefile.am

@@ -76,6 +76,7 @@ versinclude_HEADERS = 				\
 	include/starpu_deprecated_api.h         \
 	include/starpu_hash.h			\
 	include/starpu_rand.h			\
+	include/starpu_disk.h			\
 	include/starpu_cublas.h			\
 	include/starpu_driver.h			\
 	include/starpu_stdlib.h			\