[CDBI] Addition of store method

[Carlos Vicente]

> Toward the end of last year I found myself needing a method to insert or
> update a record depending on if that record already existed.  I thought I
> had seen such a method called store in other systems such as Class::DBI so I
> searched around trying to find if someone had talked about this type of
> thing for Class::DBI before.

I find that same use case many times in my code.  Having such a method
inside CDBI would be useful.

This is not speed-related, though.

cv