Pull/Fetch: should respect the 'skipFetchAll' option

Git offers a configuration option named skipFetchAll (available since Git v1.6.6) that causes commands to process all repositories (git fetch --all and git remote update) to ignore remotes having this setting.

When fetching all remotes (either interactively from the Pull button with Fetch from all remote option checked, or from Background fetch), SmartGit should respect Git's skipFetchAll config option.