checkout,merge: loosen overwriting untracked file check based on info/exclude

Back in 1127148 (Loosen "working file will be lost" check in
Porcelain-ish - 2006-12-04), git-checkout.sh learned to quietly
overwrite ignored files. Howver the code only took .gitignore files
into account.

Standard ignored files include all specified in .gitignore files in
working directory _and_ $GIT_DIR/info/exclude. This patch makes sure
ignored files in info/exclude can also be overwritten automatically in
the spirit of the original patch.

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

builtin/checkout.c

@@ -401,7 +401,7 @@ static int merge_working_tree(struct checkout_opts *opts,
 		topts.fn = twoway_merge;
 		topts.dir = xcalloc(1, sizeof(*topts.dir));
 		topts.dir->flags |= DIR_SHOW_IGNORED;
-		topts.dir->exclude_per_dir = ".gitignore";
+		setup_standard_excludes(topts.dir);
 		tree = parse_tree_indirect(old->commit ?
 					   old->commit->object.sha1 :
 					   (unsigned char *)EMPTY_TREE_SHA1_BIN);

builtin/merge.c

@@ -708,7 +708,7 @@ int checkout_fast_forward(const unsigned char *head, const unsigned char *remote
 	memset(&t, 0, sizeof(t));
 	memset(&dir, 0, sizeof(dir));
 	dir.flags |= DIR_SHOW_IGNORED;
-	dir.exclude_per_dir = ".gitignore";
+	setup_standard_excludes(&dir);
 	opts.dir = &dir;
 
 	opts.head_idx = 1;