much improved test and real fix for FAT symlink loss on conflicted merge

I think that 751f496c11 didn't quite manage
to actually fix the bug, although I have not checked since its "fix" got
redone.

The test suite now actually checks the file staged in git is a symlink,
rather than relying on the bug casing a later sync failure. This seems a
more reliable way to detect it, and probably avoids a heisenbug in the test
suite.

Command/Sync.hs

@@ -434,13 +434,14 @@ resolveMerge' u
 		d <- fromRepo gitAnnexMergeDir
 		l <- liftIO $ dirContentsRecursive (d </> item)
 		if null l
-			then go (d </> item)
-			else mapM_ go l
+			then go d (d </> item)
+			else mapM_ (go d) l
 	  where
-	  	go f = do
+	  	go d f = do
 			v <- getAnnexLinkTarget f
+			let worktreef = makeRelative d f
 			case v of
-				Just target -> stageSymlink f
+				Just target -> stageSymlink worktreef
 					=<< hashSymlink target
 				Nothing -> noop