[Dbix-class] Code Review - Duplicated columns with 'having'

[Peter Rabbitson]

On Wed, Feb 13, 2013 at 02:42:24PM -0200, André Walker wrote:
> Hello,
> 
> I have run into a bug when using an aggregate function and setting two or more
> possible values to the same column in the 'having' clause.
> 

(As per https://rt.cpan.org/Public/Bug/Display.html?id=83305#txn-1180741)

Excellent diagnostics, fix and execution (tested, documented, etc). 
Patches like this rekindle my faith in sane developers ;)

Merged to master with minimal changes (renamed couple variables, 
referenced the RT in the changelog)

Cheers