Move blocking multitry save code into mapihelp

* src/revert.cpp (finalize_mapi): Remove wait code.
* src/mapihelp.cpp (mapi_do_save_changes): Try multiple times.

I randomly don't get failures saving back to mapi. Just happens
in encryption for send. Blocking the UI is not nice but usally
saving works after 1-5 tries. I've seen it as early as one try
and as much as 5.