Adding support for --log-after

[Amir Goldstein]

Hi Wayne,

This is my first time contributing to rsync.

I've sent a pull request for a feature that was done for $work:
https://github.com/WayneD/rsync/pull/442

To quote the commit message:
"This mode is useful when a process is monitoring the log for
post-processing of transferred files."

I have more contributions to make after this small one goes through,
mainly around performance and functionality of syncing files between
cifs mounts, which is the main use case of my employer.

I was wondering if there is anything else I am required to do,
besides submitting the PR.

Thanks,
Amir.