Add indirection to allow switching policy builder implementations
Extract "expand node" policy builder to new file
Add Policyfile-based policy builder for chef-client

NB: This is experimental and a bit of a hack. There is no server-side
support, so interactions with the server are coded in a "compatibility
mode" using data bag items and Chef 11 style cookbook version APIs.

The Policyfile PolicyBuilder uses a single document from the server as
the authoritative cookbook version set and expanded run list. Enabling
it will disable support for environments and roles. In addition,
chef-solo and override run lists are currently unsupported, though they
could be supported in the future.
Allow policyfile feature to be enabled in config
Update error messaging in Policyfile policy builder
Fix incompatibilites between node expansion and policyfile
Fix Policyfile tests for ruby 1.8
Merge branch 'policyfile-support'

https://tickets.opscode.com/browse/CHEF-4984