[Dbix-class] Fix memleak for long-lived resultsets.

[Vladimir Timofeev]

I made pull request with quick fix on github
https://github.com/dbsrgits/dbix-class/pull/29

Quote:
It is a recursive attributes hash chain when call search on the same
resultset many times. It looks like pseudo-leak with long-lived resultsets.

In our application (that long-lived daemon) we use something like this:

sub periodic_refresh {
  state $rs = $schema->resultset('ServerBackend')->search({status=>'active'},{order_by=>'me.id',prefetch=>'Server'});
  my @fresh_backends = $rs->all; # now we use this workaround:
$rs->search; but it is slower because new resultset created on every
iteration
  # other refresh logic
}

Please review, and apply if possible! ;-)

--
Vladimir Timofeev <vovkasm at gmail.com>