Always checkout with case sensitive iterator

On a case-insensitive filesystem, we need to deal with case-changing
renames (eg, foo -> FOO) by removing the old and adding the new,
exactly as if we were on a case-sensitive filesystem.

Update the `checkout::tree::can_cancel_checkout_from_notify` test, now
that notifications are always sent case sensitively.

CHANGELOG.md

@@ -145,3 +145,6 @@ v0.21 + 1
 * git_treebuilder_create now takes a repository so that it can query
   repository configuration.  Subsequently, git_treebuilder_write no
   longer takes a repository.
+
+* git_checkout now handles case-changing renames correctly on
+  case-insensitive filesystems; for example renaming "readme" to "README".

src/checkout.c

@@ -2474,7 +2474,7 @@ int git_checkout_tree(
 	if ((error = git_repository_index(&index, repo)) < 0)
 		return error;
 
-	if (!(error = git_iterator_for_tree(&tree_i, tree, 0, NULL, NULL)))
+	if (!(error = git_iterator_for_tree(&tree_i, tree, GIT_ITERATOR_DONT_IGNORE_CASE, NULL, NULL)))
 		error = git_checkout_iterator(tree_i, index, opts);
 
 	git_iterator_free(tree_i);

tests/checkout/tree.c

@@ -645,14 +645,7 @@ void test_checkout_tree__can_cancel_checkout_from_notify(void)
 	cl_git_fail_with(git_checkout_tree(g_repo, obj, &opts), -5555);
 
 	cl_assert(!git_path_exists("testrepo/new.txt"));
-
-	/* on case-insensitive FS = a/b.txt, branch_file.txt, new.txt */
-	/* on case-sensitive FS   = README, then above */
-
-	if (git_path_exists("testrepo/.git/CoNfIg")) /* case insensitive */
-		cl_assert_equal_i(3, ca.count);
-	else
-		cl_assert_equal_i(4, ca.count);
+	cl_assert_equal_i(4, ca.count);
 
 	/* and again with a different stopping point and return code */
 	ca.filename = "README";
@@ -662,11 +655,7 @@ void test_checkout_tree__can_cancel_checkout_from_notify(void)
 	cl_git_fail_with(git_checkout_tree(g_repo, obj, &opts), 123);
 
 	cl_assert(!git_path_exists("testrepo/new.txt"));
-
-	if (git_path_exists("testrepo/.git/CoNfIg")) /* case insensitive */
-		cl_assert_equal_i(4, ca.count);
-	else
-		cl_assert_equal_i(1, ca.count);
+	cl_assert_equal_i(1, ca.count);
 
 	git_object_free(obj);
 }