Emit only valid XML characters

Emit only valid XML characters

Previously output XML files could contain illegal characters.
Some of these characters could be encoded, and others should
not be output at all.

This change will attempt to encode characters if they are not
printable or are special. Note that if a test contains a UTF-8
charater it will not be printed out accurately.

In order to get the tests for encoding XML characters to work,
the characters separating fields in a shell variable needed to
be changed. Originally white space would separate fields,
meaning shell would eat the extra whitespace in the tests.
Because of the change, the xml output test needed to be
reworked to not rely on white space field separators.
Additionally, the printf program is used to properly un-escape
strings used in the tests.

git-svn-id: svn+ssh://svn.code.sf.net/p/check/code/trunk@1225 64e312b2-a51f-0410-8e61-82d0ca0eb02a