More secure vendorTxCode and CURL options support

The default vendorTxCode now uses a longer and less predictable random component. The vendorTxCode is now 40 ASCII characters long. You can still supply your own vendorTxCode as has always been the case - this is just the fall-back for when you don't.

It is now possible to supply additional arguments to the CURL service, which is needed in some hosting situations.