Detect cycles in definitions

[lptr]

Example:

interface TextBase {
    void insertFormattedText(int offset, Text text)
}

interface Text extends TextBase {
}

This generates typedefs on the caller side where TextBase refers to Text (of course), and that is not allowed in Haxe. Spaghetti should throw an error in this case.

[lptr]

Fix this with the AST.