support parsing numeric git configs as bool

I'm not sure if git documents it aside from 0 and 1, but any integer
can be interpreted as a bool by it. Doing the same in git-annex is good
for consistency. Also, I am planning a config that starts out as a
numeric range, but will later transition to a simple bool (hopefully),
which this interpretation supports well.

Git/Config.hs

@@ -186,6 +186,10 @@ isTrueFalse' (ConfigValue s)
 	| s' == "0" = Just False
 	| s' == "" = Just False
 
+	-- Git treats any number other than 0 as true,
+	-- including negative numbers.
+	| S8.all (\c -> isDigit c || c == '-') s' = Just True
+
 	| otherwise = Nothing
   where
 	s' = S8.map toLower s