Unify pkt-line error handling and refactor smart-http

This is a reroll of js/smart-http-detect-remote-error that also includes a fixed version of ms/proto-err-packet-anywhere [1].

The first patch clarifies the use of ERR messages in the pkt-line protocol and unifies error handling in pkt-line.c

The second patch refactors smart-http discovery in remote-curl.c. Among other improvements, it makes more use of the pkt-line functions, which allows us to catch remote errors that were previously ignored.

The third patch makes the version check in remote-curl more strict.

The final patch adds a test to verify that the fix in patch #2 does actually catch remote HTTP errors.

[1]: https://public-inbox.org/git/[email protected]/

Jeff King (2):
remote-curl: refactor smart-http discovery
remote-curl: tighten "version 2" check for smart-http

Josh Steadmon (1):
lib-httpd, t5551: check server-side HTTP errors

Masaya Suzuki (1):
pack-protocol.txt: accept error packets in any context

 Documentation/technical/pack-protocol.txt | 20 ++---
 builtin/archive.c                         |  2 -
 connect.c                                 |  3 -
 fetch-pack.c                              |  2 -
 pkt-line.c                                |  4 +
 remote-curl.c                             | 93 ++++++++++++++---------
 t/lib-httpd.sh                            |  1 +
 t/lib-httpd/apache.conf                   |  4 +
 t/lib-httpd/error-smart-http.sh           |  3 +
 t/t5551-http-fetch-smart.sh               |  5 ++
 t/t5703-upload-pack-ref-in-want.sh        |  4 +-
 11 files changed, 89 insertions(+), 52 deletions(-)
 create mode 100644 t/lib-httpd/error-smart-http.sh

2.20.0.rc2.403.gdbc3b29805-goog