[svn r328] Fixed an issue with interfaces where the vtable type of a interface implemented could be invalid. Fixes several tango modules like, FileStream, ServerSocket and most tina cluster modules :)

module bug40;

char[] func(void* p)
{
    return null;
}

void main()
{
    char[] function(void*) fp = &func;
    assert(fp(null) is null);
}