Commit a2e6e0ea0e947954836b27572e753c7f95e5a1f4

Edward Thomson 2018-11-06T14:15:43

transport: allow cred/cert callbacks to return GIT_PASSTHROUGH Allow credential and certificate checking callbacks to return GIT_PASSTHROUGH, indicating that they do not want to act. Introduce this to support in both the http and ssh callbacks. Additionally, enable the same mechanism for certificate validation. This is most useful to disambiguate any meaning in the publicly exposed credential and certificate functions (`git_transport_smart_credentials` and `git_transport_smart_certificate_check`) but it may be more generally useful for callers to be able to defer back to libgit2.