[Libguestfs] [PATCH nbdkit v2 01/11] server: Implement NBD_FLAG_CAN_MULTI_CONN.

For existing commits, this is almost identical to v1, except that I updated some commit messages and reordered the commits in a somewhat more logical sequence. The main changes are the extra commits: [06/11] plugins: Return NBD_FLAG_CAN_MULTI_CONN from some readonly plugins. - Readonly plugins that can set the flag unconditionally. [09/11] partitioning: Return NBD_FLAG_CAN_MULTI_CONN. [10/11] data, memory: Return NBD_FLAG_CAN_MULTI_CONN. - Writeable plugins where it should be safe to set the flag always. [11/11] memory, data: Use fine-grained locking and - Let's play with locking. That last commit should be "data, memory: ..." Rich.