Batch API tweaks

Deploy module looks terrific ! Thanks Greg.

A couple minor remarks regarding the use of batch API :
- Your batch ops (deploy_plan_check_item_batch, deploy_item_batch) don't take tha batch $context as an argument, thus $context['message'] = t('Now processing %item', array('%item' => $description)); has no effect. Batch API provides $context as the last parameter of the op functions, you can take it by ref and add messages and results.
- Using $context['sandbox'] is only relevant for multipass operations (one single operation that gets called repeatedly until it declares itself as 'finished'. Not your case, so you can drop those lines.