(#3) Add an anchor type to provide containment

(#3) Add an anchor type to provide containment

With Puppet 2.6.x we do not have a way to specify containment
relationships.  In the use case of class ntp { } declaring
ntp::{package,config,service} classes, the ntp class itself should allow
the user to specify before and require relationships to the main ntp
class.

The anchor resource type allows module authors to close the loop on
classes composing the main top level module.  For example:

    class ntp {
      class { 'ntp::package': }
      -> class { 'ntp::config': }
      -> class { 'ntp::service': }
      # These two resources "anchor" the composed classes
      # such that the end user may use "require" and "before"
      # relationships with Class['ntp']
      anchor { 'ntp::begin': } -> class { 'ntp::package': }
      class { 'ntp::service': } -> anchor { 'ntp::end': }
    }

Using this pattern, the module user may then simply declare relationships to
the ntp class as they expect:

    class { 'ntp': } -> class { 'mcollective': }
    # OR
    class { 'mcollective': } -> class { 'ntp': }