Generic push support for dumb transport protocols.
Since there are no Git-specific smarts on the remote side of the connection the client side must handle everything on its own. The generic push support requires being able to delete, create and overwrite files on the remote side, as well as create any missing directories (if necessary). Typically this can be handled through an FTP style protocol. Objects not on the remote side are uploaded as pack files, using one pack file per invocation. This simplifies the implementation as only two data files need to be written to the remote repository. Push support supplied by this class is not multiuser safe. Concurrent pushes to the same repository may yield an inconsistent reference database which may confuse fetch clients. A single push is concurrently safe with multiple fetch requests, due to the careful order of operations used to update the repository. Clients fetching may receive transient failures due to short reads on certain files if the protocol does not support atomic file replacement. see WalkRemoteObjectDatabase. 