Detect invalid submodule names from script?

[Joachim Durchholz]

Hi all

I'm hacking some script that calls into git, and I need to detect 
whether a repository was configured with a submodule name that will work 
on "git submodule init" and friends.
I *can* run a git init and see whether it works, but I need to be 100% 
sure that the error was due to an invalid submodule name and not 
something else. Bonus points for every version of git for which it works.

Any suggestions?
Thanks!

Regards,
Jo