Re: [PATCH v5 0/3] config: allow overriding global/system config

> this is the fifth version of my patch series to provide a way of
> overriding the global system configuration.
> 
> Changes to v4:
> 
>     - Readded the call to `git_config_system()`, which I've previously
>       dropped by accident. I didn't move it into the new
>       `git_system_config()` function as it would change semantics of
>       `git config --system`.
> 
>     - Added a testcase which verifies that GIT_CONFIG_NOSYSTEM and
>       GIT_CONFIG_SYSTEM properly interact with each other: if
>       GIT_CONFIG_NOSYSTEM is set, no system-level configuration shall be
>       read. This is different than the tests for `git config --system`
>       which used to and still does ignore GIT_CONFIG_NOSYSTEM.
> 
>     - Small fixups for another testcase to drop needless redirects and
>       the `sane_unset` of GIT_CONFIG_NOSYSTEM.