squiz.FunctionDeclarationSniff not working with special words

Functions which name is one of these:
* parent
* self
* false
* true
* null

trigger the error ```Expected "function abc(...)"; found "function abc(...)"```

The error is a little bit misleading, but the cause of the error is that the AbstractPatternSniff expects T_STRING for the function name. In the above cases its T_PARENT, T_SELF, ...

I'm not yet sure how to fix that properly.
This PR is only the failing tests.