init-db: document existing bug with core.bare in template config

The comments in create_default_files() talks about reading config from
the config file in the specified `--templates` directory, which leads to
the question of whether core.bare could be set in such a config file and
thus whether the code is doing the right thing.  It turns out, that it
doesn't; it unconditionally ignores core.bare in the config file in any
--templates directory.  It is not clear to me that fixing it can be done
within this function; it seems to occur too late:
  * create_default_files() is called by init_db()
  * init_db() is called by both builtin/{clone.c,init-db.c}
  * both callers of init_db() call set_git_work_tree() before init_db()
and in order to actual affect whether a repository is bear, we'd need to
somewhere reset these values, not just the is_bare_repository_cfg
setting.

I do not want to open this can of worms at this time; I'm trying to
clean up some headers, for which I need to move some functions, for
which I need to clean up some globals, and that's far enough down the
rabbit hole.  So, simply document the issue with a careful TODO comment
and a few testcases.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t1301-shared-repo.sh

@@ -52,6 +52,28 @@ test_expect_success 'shared=all' '
 	test 2 = $(git config core.sharedrepository)
 '
 
+test_expect_failure 'template can set core.bare' '
+	test_when_finished "rm -rf subdir" &&
+	test_when_finished "rm -rf templates" &&
+	test_config core.bare true &&
+	umask 0022 &&
+	mkdir -p templates/ &&
+	cp .git/config templates/config &&
+	git init --template=templates subdir &&
+	test_path_exists subdir/HEAD
+'
+
+test_expect_success 'template can set core.bare but overridden by command line' '
+	test_when_finished "rm -rf subdir" &&
+	test_when_finished "rm -rf templates" &&
+	test_config core.bare true &&
+	umask 0022 &&
+	mkdir -p templates/ &&
+	cp .git/config templates/config &&
+	git init --no-bare --template=templates subdir &&
+	test_path_exists subdir/.git/HEAD
+'
+
 test_expect_success POSIXPERM 'update-server-info honors core.sharedRepository' '
 	: > a1 &&
 	git add a1 &&