[devtools] Use XMLValidator instead deprecated SaxOnlyValidator
The renaming was introduced in 198fdadafed6.o
This prevent a meta class conflict introduced by logilab-common 0fcd2e050621.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html