git fetch workflow improvements

Hi,

I have some ideas on improvements I would like to make to git fetch. I am not familiar with the implementation details of builtin-fetch.c and friends, and having a brief look at the implementation I am unsure how to proceed.

The ideas for improvements I have are:

    1.  When running `git fetch` on a bare repository that does not
have a remote called 'origin', fetch fails. I would like this to pick
up the first remote entry in the config file.

    2.  When mirroring a repository such as the Linux kernel and its
stable repositories in the same git repository, it would be useful to
be able to fetch the latest data from all the remotes that you are
tracking in the config file. I envision this being done by running
`git fetch -all`.

    3.  When fetching, if everything is up-to-date, display a message saying so.

- Reece