Replacement for is_function_available

stdlib has a function called is_function_available. This function was deprecated in favour of validate_legacy which is, in my opinion, not really an alternative for Puppet > 4 only setups.

It would be great if we could get a proper replacement which works with Puppet 3x, 4x and native functions.

henrik.lindberg suggested to create a function "is_defined" which takes a a resources type (e.g. "function") as first parameter and a resource name (e.g. inline_epp) as second parameter.

This would allow to extend the function slowly to all kind of resources.