Httpclient internally stores a copy of the certificate_check callback and
payload. When connecting via HTTPS, and if the server sends back
"Connection: close" after the first request, the following request would
attempt to re-use the httpclient and call the (now outdated) callback. In
particular for pygit2 this is a problem, since callbacks / payloads are only
valid for the duration of a libgit2 call, leading to a ffi.from_handle()
error and crashing the Python interpreter.

The experimental function signature is only available when
`GIT_EXPERIMENTAL_SHA256` is enabled.

`git_oid`s now have a type, and we require the oid type when creating
the object id from creation functions.

In preparation for SHA256 support, `GIT_OID_RAWSZ` and `GIT_OID_HEXSZ`
need to indicate that they're the size of _SHA1_ OIDs.

Co-authored-by: Edward Thomson <ethomson@github.com>

6fc6eeb66c40310086c8f059cae41de69ad4c6da removed
`git_transport_smart_proxy_option`, and there was nothing added to
replace it. That made it hard for custom transports / smart
subtransports to know what remote connect options to use (e.g. proxy
options).

This change introduces `git_transport_smart_remote_connect_options` to
replace it.

Mistakenly `&&` when we should have `||`d.