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

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>