Class inheritance loop

[hexagonrecursion]

The compiler should reject class inheritance loops, but it does not.

1. Compile this code (note: does not work if you skip this step):

public class Foo
{
}

public class Bar extends Foo
{
}

extern void New()
{
}

2. Add extends Bar and compile again - the compilation is successful:

public class Foo extends Bar
{
}

public class Bar extends Foo
{
}

extern void New()
{
}

So far most attempts to extend this example either caused the game to hang or to crash.

[melex750]

This is related to #1015 and others. Fixed in my WIP.