Use templates to handle iovec structures that have an iov_base member of

type char*.


[SVN r48525]

libs/asio

@@ -1 +1 @@
-Subproject commit c60ebedd283187d9bf9f0acc4029dd1972033b72
+Subproject commit 687fe8806f144d38ef95d009853e34acb0d6582c