Added xml box write test with utf-8 content.  #131
XML text now constructed via utf-8, not ascii.  #131
Printing of XML and UUID boxes with non-ascii characters only fully supported in 3.x

In 2.x, the XML contents will be printed as entity references instead.
It's just too difficult to get both 2.x and 3.x to be entirely consistent,
and so 3.x gets the preferential treatment.  Closes #131.
Merge branch 'issue131' into devel