> The forward compatibility on 2.7.1 version here is on the basis that
> someone in 2.7 might be relying on Exception raised for Unicode string
> "for the quote function".

Again, the problem isn't compatibility. It is, simply, that we shouldn't
add new features in a bugfix branch.

> The Second point, as this is leading to an API change we should not
> have it 2.7.1
> 
> It would be unfortunate, if we revert the patch on this account only. 

Let me put it differently: if this rule didn't exist, there would be no
point in having bugfix branches, since everyone would commit their
favourite new features to bugfix branches.

There are many things which were too late for 2.7, and nobody is trying
to make a case of adding them to 2.7.1.

> I don't know if we have never adopted this approach (of changing API
> in backward compatible manner) for anything other than the security
> bug fixes alone.

We have done it a couple of times in early 3.0 and even 3.1 versions,
but that was really exceptional, and 3.x allowed us to relax some of the
rules since it was so little used at the time.