Pass --no-textconv when running git diff internally

Seems that --no-ext-diff and -c diff.external= are not enough to disable
external diff command when gitattributes textconv specifies it.

I'm pretty sure that --no-ext-diff and -c diff.external= are not both
needed, but not 100%. Something about -G may need the latter to fully
disable diffs in some cases. So kept that part as it was.

Sponsored-by: Dartmouth College's Datalad project

Database/Keys.hs

@@ -342,6 +342,9 @@ reconcileStaged qh = unlessM (Git.Config.isBare <$> gitRepo) $ do
 		, Param "--no-renames"
 		-- Avoid other complications.
 		, Param "--ignore-submodules=all"
+		-- Avoid using external textconv command, which would be slow
+		-- and possibly wrong.
+		, Param "--no-textconv"
 		, Param "--no-ext-diff"
 		]