Make SessionId#to_s be an alias of #public_id

[jeremyevans]

This restores backwards compatibility with code that uses the
session id.

No justification was given for making to_s raise in the commit
that changed the behavior (cc1d162).

If there is a reason to keep raising an exception, a specific
exception class and explicit error message should be used.

[ioquatix]

@jeremyevans I assume you want to backport this to 2.0.x?

[jeremyevans]

Yes, since 2.0.8 is affected.

[ioquatix]

@tenderlove I'm in agreement with @jeremyevans, so can you merge this, backport it, release 2.0.9 and 2.1.0 tomorrow? Thanks.

[rafaelfranca]

I'm ok with this change. We thought about doing it, but I think we decided to make it raise so third-party session adapters could upgrade their code.

[tenderlove]

We thought about doing it, but I think we decided to make it raise so third-party session adapters could upgrade their code.

Yes, this is the justification. As I said in another thread I should have raised a more specific exception and I really apologize.

[tanelsuurhans]

It looks like the 2.0.9 release was missed with this one.

[jeremyevans]

2.0.9 hasn't been released yet. When it is released, it will include this fix. See https://github.com/rack/rack/commits/2-0-stable

[jbcrail]

Can this be backported to 1.6.x? I upgraded recently to address a CVE, but was affected by this issue. Unfortunately, upgrading to 2.x isn't feasible in the short term.

[jeremyevans]

@jbcrail This was already backported to 1.6 at 698a060, there just hasn't been another release of 1.6 yet.