[bug] submodule --update insufficiently verbose

When a "git submodule --update" fails, e.g., due to a dirty working
directory in one of the submodules, nothing is printed out indicating
the submodule or directory in which the failure occurred.  This seems
like a usability bug to me.

Thanks,

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com