Fix error in write_sparse() on incomplete write.

Fix a problem where sparse_seek could get left non-zero when we
did not finish writing all the data that would take us to that
sparse gap.  Issue pointed out by David Taylor.
Fix the visit-all-patches path.
Mention latest news.
Flush write buffer on an aborted in-place transfer.
Remove unused var.
Preparing for release of 3.1.0
Prepare repository for more development.
A few more new options that rsync 3.1.0 can pass.
Don't forget about --debug and --info for rrsync.