to handle CDRom devices with no device name
* tests/sexpr2xmltest.c tests/xml2sexprtest.c
  tests/sexpr2xmldata/sexpr2xml-no-source-cdrom.sexpr
  tests/sexpr2xmldata/sexpr2xml-no-source-cdrom.xml
  tests/xml2sexprdata/xml2sexpr-no-source-cdrom.sexpr
  tests/xml2sexprdata/xml2sexpr-no-source-cdrom.xml: added regression
  tests for this case based on Nobuhiro Itou test inputs.
Daniel