ContributionProcessor.php maps "source" field differently for PayPal and Google Checkout

ContributionProcessor.php maps Google Checkout's item-name field to CiviCRM's note field. A more appropriate mapping would be:

'item-name' => 'source'
'item-description' => 'note'

Changing it in this way seems more intuitive to me, and furthermore makes it consistent with the existing mapping for PayPal, which maps the item name (l_name0) to source:

'l_name0' => 'source'

Trival patch:

http://code.creativecommons.org/viewgit/civicrm.git/commit/?h=cc_production_3.3.5&id=ae2ad8431a3914579486dd797d10bfa19128d7c3