Find all class objects in all modules.
    @param modules: the modules to search
    @ptype modules: iterator of modules
    @return: found classes
    @rytpe: iterator of class objects

def get_plugins(modules, classobj):
    """Find all class objects in all modules.
    @param modules: the modules to search
    @ptype modules: iterator of modules
    @return: found classes
    @rytpe: iterator of class objects
    """
    for module in modules:
        for plugin in get_module_plugins(module, classobj):
            yield plugin