SCM Syncer: SVN and Git

Hi there!

Please find attached a pull request that adds support for backing up SCMs (both with Git and SVN) into Backup.

I have tried to mimic the changes you made to my previous pull request (RSync::Push-Pull-etc). For example, this version uses a "repositories" property (alias for "directories") like so:

    Backup::Model.new(:hdl_make, 'Description for hdl_make') do
      sync_with SCM::Git do |git|
        git.ip           = "example.com"
        git.path         = "backups/git"
        git.repositories do
          add "/misc/repo-1.git"
          add "/foo/bar/repo-2.git"
        end
      end
    end

This will backup the repositories git://example.com/misc/repo-1.git and git://example.com/foo/bar/repo-2.git inside the folder backups/git.

Best regards,

Enrique