Comment 9 for bug 98382

I've prepared some patches implementing this, but would like to ask for comments before committing something as core as this.

I also added the requirement that, except for not being able to commit, a doomed transaction behaves exactly the same as an active transaction.

The first patches implement a transaction.doom() function:

 http://lentejasverdes.ath.cx/stuff/zope/patch.transaction
 http://lentejasverdes.ath.cx/stuff/zope/patch.zopeapp

These two then implement an isDoomed() function:

 http://lentejasverdes.ath.cx/stuff/zope/patch.transaction2
 http://lentejasverdes.ath.cx/stuff/zope/patch.zopeapp2