init: Configure .git/info/attributes to use git-annex as a smudge filter.

Note that this changes the default behavior of git add in a newly
initialized repository; it will add files to the annex.

Don't like that this could break workflows, but it's necessary in order for
any pointer files in the repo to be handled by git-annex.

Config.hs

@@ -95,3 +95,16 @@ configureSmudgeFilter :: Annex ()
 configureSmudgeFilter = do
 	setConfig (ConfigKey "filter.annex.smudge") "git-annex smudge %f"
 	setConfig (ConfigKey "filter.annex.clean") "git-annex smudge --clean %f"
+	lf <- Annex.fromRepo Git.attributesLocal
+	gf <- Annex.fromRepo Git.attributes
+	lfs <- readattr lf
+	gfs <- readattr gf
+	liftIO $ unless ("filter=annex" `isInfixOf` (lfs ++ gfs)) $ do
+		createDirectoryIfMissing True (takeDirectory lf)
+		writeFile lf (lfs ++ "\n" ++ stdattr)
+  where
+	readattr = liftIO . catchDefaultIO "" . readFileStrictAnyEncoding
+	stdattr = unlines
+		[ "* filter=annex"
+		, ".* !filter"
+		]