Changed Backups.md to use force-update post 1.2

Added a version section for post-1.2 which uses the `riak-admin cluster
force-replace` syntax instead of the deprecated `riak-admin reip` scheme
for remaned nodes.
Reworked example lead-in paragraph
Merge remote-tracking branch 'source/master'
Merge pull request #166 from angrycub/master

Backups cookbook to use `force-replace` for riak 1.2