Git client

Hi, 9fans.

I ported official Git client to 9legacy. It's very early version yet,
but it can do basic commands such as fetch, pull, log, add, and commit
-m.

Probably there are many bugs. Some of them might be results from a
issue of 8c that don't initialize rest fields of struct and union with
zero if field names are specified.

x86 binaries are available here:
https://lufia.org/git-386.tgz

Source codes:
- https://github.com/0intro/plan9-contrib/pull/6
- https://github.com/0intro/plan9-contrib/pull/7
- https://github.com/madler/zlib/pull/398
- https://github.com/libressl-portable/portable/pull/510
- https://github.com/libexpat/libexpat/pull/242
- https://github.com/curl/curl/pull/3701
- https://github.com/lufia/git

- kadota