Authorize.net ARB name can be too long

The XML schema for Authorize.net Automated Recurring Billing limits the "name" field for the subscription to 50 characters. Contribution pages with long names cause donors to get the following error when they try to make a recurring contribution:

"E00003: The 'AnetApi/xml/v1/schema/AnetApiSchema.xsd:name' element is invalid - The value 'Online Contribution: Support the use of contribution pages with really long names' is invalid according to its datatype 'String' - The actual length is greater than the MaxLength value."

I've attached a patch to templates/CRM/Contribute/Form/Contribution/AuthorizeNetARB.tpl simply truncating the name to 50 characters. The result for the example above would be a subscription named "Online Contribution: Support the use of contrib..."