bug#56682: feature/improved-locked-narrowing 9dee6df39c: Reworked locked narrowing.

[Gregory Heytings]

> Please describe the bug you discovered and the changes made to fix it 
> (and maybe also alternatives if you considered them).

The bug is that narrowing locks were not saved and restored by 
save-restriction as they were supposed to be.  AFAIK there are no 
alternatives to what I did.

I did on purpose separate that bugfix (commit 1 on the branch) from the 
renaming ones (commits 2-5), the documentation one (commit 6) and the one 
that adds a test (commit 7) to make the reviewing task easier.

> Also, did you test this both with and without native-compilation?

Yes, without and with native-compilation.  Though with native-compilation 
I only checked with the complete changeset.

> Andrea, could you please see if the changes on that branch are okay as 
> far as native-compilation is concerned?

Note that the only commit you should check is 7691a84d2a.