Fixed error where implemented interfaces that have not been parsed will ...

[pgraham]

...be ommitted from output.

To further illustrate the problem consider the following files parsed in the order listed below:

1. MyInterface1.php:

   interface MyInterface1 { ... }

2. MyClass.php:

   class MyClass implements MyInterface1, MyInterface2 { ... }

3. MyInterface2.php

   interface MyInterface2 { ... }

In the described scenario, the list of implemented interfaces for MyClass will not contain MyInterface1