enable "no-done" extension only when fetching over smart-http

When 'no-done' protocol extension is used, the upload-pack (i.e. the server side) process stops listening to the fetch-pack after issuing the final NAK, and starts sending the generated pack data back, but there may be more "have" send by the latter in flight that the fetch-pack is expecting to be responded with ACK/NAK. This will typically result in a deadlock (both will block on write that the other end never reads) or SIGPIPE on the fetch-pack end (upload-pack will finish writing a small pack and goes away). Disable it unless fetch-pack is running under smart-http, where there is no such streaming issue. Signed-off-by: Junio C Hamano <gitster@pobox.com> Acked-by: Shawn O. Pearce <spearce@spearce.org>