Ignore submodules that are defined in .gitmodules but are checked in as directories.

Pulls in gitlab_git 7.1.10 which contains gitlab_git!26 (merged).

Fixes #1439 (closed) and https://github.com/gitlabhq/gitlabhq/issues/9140

cc @stanhu

Thanks, @DouweM!

Reassigned to @dzaporozhets

Status changed to merged

mentioned in commit 61ebd14d