Send/receive v3 update

[kdave]

• send progress in the stream
• send fallocate/holes effectively
• fsverity support
• encryption support (if implemented)
• clones within one file

[kdave]

Todo item: look what synology does in their private send stream and pick it eventually.

[kdave]

Moving v3 to 6.2 (ie. not planned for 6.1, which is now open).

[kdave]

Moving v3 to 6.3 (ie. not planned for 6.2, which is now open).