Control: retitle -1 want better error reporting when there are submodules
dgit does not work with submodules. See #726953.
Sam Hartman writes ("Bug#871908: dgit fails to work when .git is a reference
not a directory"):
> If you git clone --recursive a project including submodules, you tend to
> get all the submodule git directories under .git/modules in the master
> git directory.
> mkdir .git/dgit: Not a directory at /usr/share/perl5/Debian/Dgit.pm line
This is not a very useful error message.
Also, there is a potential risk that fixing dgit to work with git
worktrees (#868515) may result in a situation where dgit would fail to
properly notice submodules and might carry on and do something
actually dangerous rather than merely confusing.