Updating GitLab url parsing; fix authed list_refs

[dgkf]

This PR is intended to fix #328 with a few other related fixes

• Updates parsing for GitLab remotes, which currently is forgetting a / between the host and "username". Unlike GitHub, GitLab allows arbitrary nesting of groups:	Service	Style
  GitHub	username/repo
  GitLab	group/subgroup/subsubgroup/project

  This throws a wrench in the subdir parsing. To allow a subdir, I added a /-/ separator:
  group/subgroup/project/-/sub/dir@ref /-/ is a reserved name used for other server paths, so there's no risk of conflict with project paths.

• Calls to /info/refs?service=git-upload-pack require authentication, which is currently ignored. I added this authentication to async_git_list_refs_v2 and async_git_send_message_v2, necessary for solving package dependencies.

Let me know if I'm on the right track, or if you think this is better solved some other way.

[dgkf]

Since GitLab can have arbitrarily nested projects and some alternative syntax would be needed to differentiate user/repo/sub/dir from /group/subgroup/subgroup2/subgroup3, would an alternative syntax more akin to Authors@R be up for consideration?

Remotes:
  list(name = "pkg", type = "gitlab", url = "https://acme.co/a/b/c.git", subdir = "x/y/z", ref = "dev")

I appreciate that the current string style is quite brief, but maybe something more explicit would be a nice fallback?

[gaborcsardi]

Thanks! I changed this a bit to add auth to all git HTTP queries. There is two things to do still:

• cache unsuccessful gitcreds queries, because they take about 0.2s now, and could take even longer with different git credential helpers,
• write tests.

[gaborcsardi]

would an alternative syntax more akin to Authors@R be up for consideration?

That is not great, because other tools will interpret the Remotes field differently. It also does not play well with other, non-R tools that try to use the DESCRIPTION file.

This throws a wrench in the subdir parsing. To allow a subdir, I added a /-/ separator: group/subgroup/project/-/sub/dir@ref

Yes, this could work.

[gaborcsardi]

Actually, some the git and gitlab tests are already "live", so we can update those later, and I am going to merge this now, after updating the docs.

[gaborcsardi]

Thanks you again!