loosen dependency for chef
change chef dependency in gemspec
Realms appear to be working. So far, realms are a way of talking about
related clusters. They prepend their name to the name of the clusters
within them and also allow some things (environments, common cloud
properties) to be merged into each cluster.

For example,

Ironfan.realm(:p1) do
  cloud(:ec2).bits 64

  cluster(:control) do
     # etc.
  end
  cluster(:kfk) do
     # etc.
  end
end

the realm here would result in p1_control and p1_kfk clusters with a
default cloud(:ec2).bits attribute merged in.
tidying up a bit
Version bump to 4.11.5
Regenerate gemspec for version 4.11.5
Merge branch 'jbro_realms' of https://github.com/infochimps-labs/ironfan
Version bump to 4.12.0
Regenerate gemspec for version 4.12.0
possibly neater discovery with clusters helpers
cluster_names helper for facets
adding cluster_suffxies helper for realms
Merge branch 'jbro_realms' of https://github.com/infochimps-labs/ironfan
Version bump to 4.12.1
Regenerate gemspec for version 4.12.1
moving to hashes for cluster discovery helpers
REALM cluster name helpers cleanup

Realms now have access to a cluster_suffix helper that can be used as
follows.

```
Ironfan.realm(:p1) do
  # declaration
  cluster(:control)

  # implementation
  cluster(cluster_suffix(:control)) do
    # ...
  end
end
```

cluster_suffix(suffix) always returns suffix: it is the identity
function with a twist. The twist is that it will ensure that the
cluster exists within the realm. This is to ward off typos.

In addition, components now have acccess to a cluster_name helper that
can be used as follows.

```
Ironfan.realm(:p1) do
  # declaration
  cluster(:control)

  # implementation
  cluster(cluster_prefix(:control)) do
    facet(:nfs) do
      # ...
      nfs_server
      # ...
    end

    facet(:zabbix) do
      # ...
      nfs_client{ of cluster_name(:control) }
      # ...
    end
  end
end
```

In this case, in addition to ensuring that the :control cluster exists
within this realm, cluster_name(:control) returns the full name of the
cluster: :p1_control.
Version bump to 4.12.2
Regenerate gemspec for version 4.12.2
Add blank_xfs snapshot for Tokyo.