Demonstration of uninstantiable defaulted constructor parameter injection issue.
Merge branch 'uninstantiable-defaulted-constructor-param-issue' of https://github.com/ezzatron/PHP-DI into bug/168
Simplified the test for #168
Bug #168 Default parameter values are used when a parameter is mapped to an unresolvable entry

Optional parameters that are type-hinted with interfaces should use the default parameter value if the interface is not mapped to a concrete class.
Else that makes autowiring pretty much useless if a class takes optionally a parameter that we don't want to specify (use default value).
Merge pull request #169 from mnapoli/bug/168

Container::has() should return false for un-mapped interfaces/abstract classes