Add git+https support.

[jszakmeister]

No description provided.

[jszakmeister]

FWIW, I modeled this after what was done in hg_https.lua. I hope it's the right approach.

[mpeterv]

LGTM, although the new file must be added to the list in Makefile.setup.inc

@hishamhm by the way, why --depth=1 is not used when fetching git+http://? 1 2

[ignacio]

@mpeterv because it depends on the git server. See this page on protocols. The old "dumb" protocol does not support the depth flag.

$ git --version
git version 1.9.5.msysgit.0
$ git clone --depth=1 http://luajit.org/git/luajit-2.0.git luajit-2.0
Cloning into 'luajit-2.0'...
fatal: dumb http transport does not support --depth

However, some git servers implement a "smart" http protocol. Github, for instance, supports the --depth flag with no problems.

$ git clone --depth=1 http://github.com/keplerproject/luarocks.git luarocks
Cloning into 'luarocks'...
remote: Counting objects: 193, done.
remote: Compressing objects: 100% (169/169), done.
remote: Total 193 (delta 16), reused 123 (delta 11), pack-reused 0
Receiving objects: 100% (193/193), 3.29 MiB | 158.00 KiB/s, done.
Resolving deltas: 100% (16/16), done.
Checking connectivity... done.

I found a way to determine whether the server is dumb or smart but it is quite convoluted.

So if we were to support this flag over these transports, maybe we could have a whitelist of known git services that support the --depth flag but I don't know if it is worth the hassle. /cc @hishamhm

(additionally, I found these notes on the Git HTTP transport documentation)