entry.c: create submodules when interesting

entry.c: create submodules when interesting

When a submodule is introduced with a new revision
we need to create the submodule in the worktree as well.
As 'submodule_move_head' handles edge cases, all we have
to do is call it from within the function that creates
new files in the working tree for workingtree operations.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>