smart-http: Really never use Expect: 100-continue

smart-http: Really never use Expect: 100-continue

libcurl may choose to try and use Expect: 100-continue for
any type of POST, not just a Transfer: chunked-encoding type.
Force it to disable this feature, as not all proxy servers support
100-continue and leaving it enabled can cause 1 second stalls during
the negotiation phase of fetch-pack/upload-pack.

In ("206b099d26 smart-http: Don't use Expect: 100-Continue") we
tried to disable this for only large POST bodies, but it should be
disabled for every POST body.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>