* Xlsx Reader External Data Validations Flag Missing
Fix#2677. This PR supersedes #2679, written by @technghiath, which lacks tests, and probably doesn't solve the problem entirely. The code causing the problem appears to be the last remnant in Xlsx Reader which calls `children` using a namespace prefix rather than a namespace. That is changed, and tests are added where the tag is unexpectedly missing, and also where it uses a non-standard namespace prefix.
* Scrutinizer
Reports 1 "new" error. It isn't, but fix it anyhow.
* Fix One Existing Scrutinizer Problem
Only remaining problem in Reader/Xlsx.
050a42db8e