This is a brown paper bag. When adding the tests, we actually failed
to verify that the config variable is heeded in git-init at all. And
when changing the original patch that marked the .git/ directory as
hidden after reading the config, it was lost on this developer that
the new code would use the hide_dotfiles variable before the config
was read.
The fix is obvious: read the (limited, pre-init) config *before*
creating the .git/ directory.
This fixes https://github.com/git-for-windows/git/issues/789
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>