avoid reading files that are not symlinks when core.symlinks=false

This hack is only needed on FAT filesystems, so there's no point in doing
it the rest of the time. And it's possible for there to be a false
positive, so it's best to avoid the hack when possible.

Annex/Link.hs

@@ -36,10 +36,13 @@ isAnnexLink file = maybe Nothing (fileKey . takeFileName) <$> getAnnexLinkTarget
  - content.
  -}
 getAnnexLinkTarget :: FilePath -> Annex (Maybe LinkTarget)
-getAnnexLinkTarget file =
-	check readSymbolicLink $
+getAnnexLinkTarget file = ifM (coreSymlinks <$> Annex.getGitConfig)
+	( check readSymbolicLink $
 		check readfilestart $
 			return Nothing
+	, check readSymbolicLink $
+		return Nothing
+	)
   where
 	check getlinktarget fallback = do
 		v <- liftIO $ catchMaybeIO $ getlinktarget file