test helpers: move test-* to t/helper/ subdirectory

This keeps top dir a bit less crowded. And because these programs are
for testing purposes, it makes sense that they stay somewhere in t/

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/helper/test-scrap-cache-tree.c

@@ -0,0 +1,17 @@
+#include "cache.h"
+#include "lockfile.h"
+#include "tree.h"
+#include "cache-tree.h"
+
+static struct lock_file index_lock;
+
+int main(int ac, char **av)
+{
+	hold_locked_index(&index_lock, 1);
+	if (read_cache() < 0)
+		die("unable to read index file");
+	active_cache_tree = NULL;
+	if (write_locked_index(&the_index, &index_lock, COMMIT_LOCK))
+		die("unable to write index file");
+	return 0;
+}