[Alg] Directives should be preserved when processing the algorithm layer

[rupertford]

The gocean/eg2 example compiles and runs an OpenACC example. To return the final values from the accelerator an OpenACC directive is manually placed in the algorithm file. However, this directive is removed after running the algorithm layer through PSyclone. This causes incorrect behaviour in the example.

[arporter]

This is also a problem if we want to use PSyclone to add profiling calipers to a code that has had OpenACC directives added to it (manually).