Allow the client to specify "sideband-all" in a fetch v2 request,
indicating that the whole response is to be multiplexed (with a sideband
indicator on every non-flush and non-delim pkt) instead of only the
packfile being multiplexed. This allows, for example, progress messages
to be sent at any point in the response.
This implements the "sideband-all" feature documented in
Documentation/technical/protocol-v2.txt in Git.
Change-Id: I3e7f21c88ff0982b1b7ebb09c9ad6c742c4483c8
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>