Ensure that binder evaluates using Puppet[:parser] = 'future'

This ensure more correct evaluation.
Fix Pupet typo
Add implicit parameter lookup for hostclass resources.

This adds implicit lookup of host class parameters via injector.
Checks DataBindings (i.e. Hiera) if there is no bound value.

Fixes tests that were mocking scope and did not expect calls to
compiler. Also adds accessor method that creates an injector if none was
created.
Add tests for implicit injection.

This adds tests that host class parameters are looked up in the
injector.
Also adds a NullInjectorImpl intended to use in future tests.