Concatenate node on print, PDF and email (Print basket)

I've seen some sites allowing to create a customized PDF or printable page using a basket / cart where putting pages in. In this way, one can print a single page or concatenate multiple pages on his/her own basket.

This module uses a single template to generate PDF, printable pages and emails: now it adopts a per-node approach, allowing to handle a single node (the first use case). I tried to transform the $print array into an array of array passing to _print_generate_node() function an array, instead a single value. With little changes, the print, printmail and printpdf URLs can be adapted as follows:

• http://example.com/print/1
• http://example.com/print/2,1

Where #2 concatenates node 2 and node 1 for print.

With this feature, a print basket can be implemented even with a javascript + cookies based tool (to store nids array) that call that URL (that generates the concatenated content) using this module.

So, the implementation of a working basket should comprehend:

• New URLs implementation and testing
• Basket tool creation for print, mail and pdf (each medium should have his own basket)

I've not tested deeply this code: it surely can be optimized and it covers only the first step. Comments and ideas for a basket tool are warmly welcomed.