Fix a potential failure to parse git config

Fix a potential failure to parse git config

Git has an obnoxious special case in git config, a line "foo" is the same
as "foo = true". That means there is no way to examine the output of
git config and tell if it was run with --null or not, since a "foo"
in the first line could be such a boolean, or could be followed by its
value on the next line if --null were used.

So, rather than trying to do such a detection, track the style of config
at all the points where it's generated.