It now works.  I changed the code to:

#needed for calling function from wizard, api.one will not work
 @api.multi
#function definition is in odoo v8 format
	def summary_report(self):
#ensure that self contains only one record
		self.ensure_one()
#get the model to query
		invoiceModel = self.env['account.invoice']
#query the model
		invoices = invoiceModel.search([
			('company_id', '=', self.company_id.id)
			])
#set the data
#ids is the list of ids, so have to pass <model>._ids
#model is the model name  <model>._name or string literal
#form is the field list, I use <model>.read() to get all fields, read() can have parameter to only read specific fields
		datas = {
			'ids': invoices._ids,
			'model': invoiceModel._name,
			'form': invoiceModel.read(),
			'context':self._context
		}
#call the report
		return {
                   'type': 'ir.actions.report.xml',
                   'report_name': 'mil_sales_report.invoice_summary_template',
                   'datas': datas
               }