error: submod: is a directory - add files inside instead
The reason is that git diff-index, which generates the first part of the
list of files updated by the tree filter, emits also the removed submodule
even if it was replaced by a real directory.
Signed-off-by: Michal Sojka <sojkam1@fel.cvut.cz> Signed-off-by: Junio C Hamano <gitster@pobox.com>