advice: don't pointlessly suggest --convert-graft-file

The advice to run 'git replace --convert-graft-file' added in
f9f99b3f ("Deprecate support for .git/info/grafts", 2018-04-29)
didn't add an exception for the 'git replace --convert-graft-file'
codepath itself.

As a result we'd suggest running --convert-graft-file while the user
was running --convert-graft-file, which makes no sense. Before:

    $ git replace --convert-graft-file
    hint: Support for <GIT_DIR>/info/grafts is deprecated
    hint: and will be removed in a future Git version.
    hint:
    hint: Please use "git replace --convert-graft-file"
    hint: to convert the grafts into replace refs.
    hint:
    hint: Turn this message off by running
    hint: "git config advice.graftFileDeprecated false"

Add a check for that case and skip printing the advice while the user
is busy following our advice.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/replace.c

@@ -495,6 +495,7 @@ static int convert_graft_file(int force)
 	if (!fp)
 		return -1;
+	advice_graft_file_deprecated = 0;
 	while (strbuf_getline(&buf, fp) != EOF) {
 		if (*buf.buf == '#')
 			continue;

t/t6050-replace.sh

@@ -461,7 +461,10 @@ test_expect_success '--convert-graft-file' '
 	printf "%s\n%s %s\n\n# comment\n%s\n" \
 		$(git rev-parse HEAD^^ HEAD^ HEAD^^ HEAD^2) \
 		>.git/info/grafts &&
-	git replace --convert-graft-file &&
+	git status 2>stderr &&
+	test_i18ngrep "hint:.*grafts is deprecated" stderr &&
+	git replace --convert-graft-file 2>stderr &&
+	test_i18ngrep ! "hint:.*grafts is deprecated" stderr &&
 	test_path_is_missing .git/info/grafts &&
 	: verify that the history is now "grafted" &&