implement autoload-do-load and use it; removing some polyfills

[KeenS]

It is not an exact implementation of autoload-do-load, but almost the same.
The behavioral differences can be observed only when the autoload fails.
In the emacs' implementation, it undoes all the definitions and provides in the load chain, but this function does not (more to say, cannot. The definition history is held only in C).
However, I think this is sufficient for polyfill for testing.

[conao3]

With the code you wrote, I can now integrate test cases into one.
Thank you very much !!