read, write: restore global `lwt_wrap_exn`
read, write: restore global `lwt_wrap_exn`

The wrapper is needed to transform `End_of_file` exceptions into
Error returns.

Signed-off-by: David Scott <bfcdf3e6ca6cef45543bfbb57509c92aec9a39fb@recoil.org>

samoht/mirage-block-unix,mirage/mirage-block-unix,djs55/mirage-block-unix