Re: Distinguish between regional undo and undo to the beginning in undo-equiv-table

[Yuan Fu]

> 
>> Then should we add a mapping for the buffer-undo-list to t at that
>> point?  Or should we just do nothing?
> 
> Good question.  I think you have a better understanding of how the equiv
> table should be filled than I do at this point, so I'd trust your judgment.

Ok, I looked into it in detail, undo-equiv-table is also used to check if the 
previous command is really an undo, alongside with checking last-command. So 
the undo record has to map to something, I decide to map it to ‘empty unless 
there is already a mapping for the record. Here is the (standalone) final 
draft. Please have a look.

Yuan

undo-in-region-3.patch
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