(#6770) Change versioning; adopt :current over :latest.
As per discussion with Luke, versions of an interface are first looked up by
requiring 'puppet/interface/{name}', and secondarily looked up by requiring
'{name}@{version}/puppet/interface/{name}' if the first failed.
A version of :current can be used to represent the version living in
'puppet/interface/{name}'.
Paired-With: Nick Lewis