Add --validate and --validate-only flags to wxrc that perform validation of the input files against the RELAX NG schema from misc/schema. Jing must be installed for this to work. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74988 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775