Make sure we debug XML load failures properly

[seansan]

See link for simple example. 1 line of ccode to add (should work aalso for Mage2)

http://www.smartsell.nl/magento-simplexml_load_string-warnings-in-the-system-log/

[magento-team]

Config validation was added to Magento2 backlog.

[magento-team]

Closed. Will be published with nearest update.