* [CHD-2954] [CHD-2549] [Performance/Scheduler/Maint] Improved the performance of the nightly maintenance scheduler job.  Previously, this was inefficiently looking for broken links between records by performing expensive table joins.
* [Devblocks/Code Cleanup] Fixed an issue where negative byte values weren't formatted by DevblocksPlatform::strToPrettyBytes().  It's common to have a negative number of bytes when computing deltas between two numbers.
* [VAs/Placeholders/XML] Fixed the 'xml_decode()' function in placeholder scripts so it doesn't attempt to convert an XML document to an array.  It now remains a SimpleXMLElement instance from PHP, which can be iterated, queried with XPath, etc.
* [VAs/Placeholders/XML] Fixed an issue with the 'xml_decode()' function in placeholder scripts where namespaced XML documents didn't always work with XPath queries.
* [VAs/Placeholders/XML] Added an 'xml_xpath()' function to placeholder scripts for querying the XML object returned by 'xml_decode()'.  This can also return attributes.
6.7-dev checkpoint