Merge branch 'test-unc-alternates'

The fix we introduced in Git for Windows will be made obsolete by a more
general fix that has been already accepted into upstream Git's `next`
branch.

But we still can introduce a regression test that verifies that this bug
will be caught very quickly, if reintroduced.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

t/t5580-clone-push-unc.sh

@@ -43,4 +43,16 @@ test_expect_success push '
 	)
 '
 
+test_expect_success 'unc alternates' '
+	tree="$(git rev-parse HEAD:)" &&
+	mkdir test-unc-alternate &&
+	(
+		cd test-unc-alternate &&
+		git init &&
+		test_must_fail git show $tree &&
+		echo "$UNCPATH/.git/objects" >.git/objects/info/alternates &&
+		git show $tree
+	)
+'
+
 test_done