Add ratcheting DTD checking to CI

.travis.yml

@@ -1,6 +1,12 @@
-script: make all
-
 addons:
   apt:
     packages:
       - xsltproc
+      - libxml2-utils
+before_install:
+  - wget -O git-ratchet https://github.com/iangrunert/git-ratchet/releases/download/v0.3.1/linux_amd64_git-ratchet
+  - chmod +x git-ratchet
+  - git fetch https://github.com/xsf/xeps.git refs/notes/*:refs/notes/*
+script:
+  - make all
+  - echo "lint,$(xmllint --nonet --noout --noent --loaddtd --valid *.xml 2>&1 | wc -l)" | ./git-ratchet check -v

Makefile

@@ -39,6 +39,9 @@ xep-%.html: $(OUTDIR)/xep-%.html ;
 dependencies: $(OUTDIR)/prettify.css $(OUTDIR)/prettify.js $(OUTDIR)/xmpp.css ;
 
 $(OUTDIR)/%.html: %.xml $(XMLDEPS) dependencies
+	# TODO: After existing issues are worked out this and the ratcheting CI build
+	#       should be removed and become an error, not just a warning.
+	xmllint --nonet --noout --noent --loaddtd --valid "$<" || true
 	xsltproc --path $(CURDIR) xep.xsl "$<" > "$@" && echo "Finished building $@"
 
 $(OUTDIR)/%.js: %.js