[Simple-support] Invalid unicode characters in XML stream

[Dawid W. <daw...@gm...>]

Niall, you asked if this is a problem in practice -- see this build
log, for example:

http://jenkins.sd-datasolutions.de/job/Lucene-Solr-4.x-Linux/1199/consoleText

it failed for exactly the reasons I mentioned -- invalid unicode
character in a throwable's message, serialized via simple-xml's model
for ANT's junit files. I think it should be fixed at some point and I
think it should be the default behavior to always produce valid XML,
no matter what the performance penalty might be.

Perhaps Formatter should be a replaceable strategy? Doesn't seem like
there are that many options there, but it could be fun too -- think of
a binary-XML formatter :) Just a thought.

Dawid