Add circuit xml validation to the loader

[jimcollins]

Currently the loader just tries to do ParseXML() on the circuit file. If the circuit file isn't valid it throws an unhelpful error of "A problem was encountered while reading the #fb_.fuseboxXMLfile# file."

If XMLValidate was run first, you would get a much more helpful error like:
"[Fatal Error] :13:9: The element type "fuseaction" must be terminated by the matching end-tag "</fuseaction>" giving you the exact error and line number where the error occured.
I'll be glad to add this if someone wants.

[scorfield]

XmlValidate?() isn't available on all the platforms that Fusebox supports, however, as an option set in index.cfm, this would be a nice enhancement (it can't be set in fusebox.xml because, well, we haven't parsed the file by the time we need to decide whether to run the validator :)

[scorfield]

Defer to 5.6.