[RFC] submodule: display progress by default

Currently, git submodule does not display operation progress unless explicitly demanded by adding the --progress option to the command. This makes a bad user experience in cases of initializing a huge submodule, as one might get an impression that something went wrong and the execution froze (which was exactly my case recently).

The help page states that this is enabled by default if stderr is directed to the terminal. This is not true. It is still required to explicitly pass this option to the command.

My proposition is, instead of updating the documentation, is to set the --progress flag to true by default, and leave the rest as-is for backward compatibility. If one does not wish to see the progress, it is possible to silence it with -q or --quiet option.

Notice that such behavior will be identical for commands like clone, which display progress unless silenced with -q or --quiet.

Also submodule--helper seems to have trouble handling the --progress option. For example, `$ git submodule update --init modulename --progress` prints `error: unknown option `progress'`, but running `$ git submodule update --init --progress modulename` works fine.

Also progress is not reported for add subcommand even with --progress option set.

Note: --progress was added to submodule with commit 6d33e1c2821.

Please let me know what you think about it.

Taking advantage of the opportunity, I would like to greet everyone - it is my first post to git's mailing list.