* src/xen/sexpr.c: Ensure () are escaped in sexpr2string
* tests/sexpr2xmldata/sexpr2xml-boot-grub.sexpr,
  tests/sexpr2xmldata/sexpr2xml-boot-grub.xml,
  tests/xml2sexprdata/xml2sexpr-boot-grub.sexpr,
  tests/xml2sexprdata/xml2sexpr-boot-grub.xml: Data files to
  check escaping
* tests/sexpr2xmltest.c, tests/xml2sexprtest.c: Add boot-grub
  escaping test case