Moving reveal.js and warn on absence

Doc/Makefile

@@ -62,7 +62,7 @@ ${BUILDROOT}/webhelp/index.html:${BUILDROOT}/${SCRIPTBASENAME}.xml
 	cd  ${BUILDROOT};\
 	${SAXONCMD} -s:${SCRIPTBASENAME}.xml -xsl:../../ws/Docbook/Extensions/Xsl/docbook2slides.xsl \
          callout.unicode=1 highlight.source=1;\
-        ln -sf /usr/share/reveal.js Slides;\
+        ln -sf ${HOME}/reveal.js Slides;\
         /usr/share/xmlmind/bin/xxetool convert ${XSLPARAM} db5.toWebHelp \
             ${SCRIPTBASENAME}_html.xml -u webhelp
 	cp -f webhelp.css ${BUILDROOT}/webhelp

Makefile

@@ -8,6 +8,9 @@ java avconv
 K := $(foreach exec,$(EXECUTABLES),\
         $(if $(shell which $(exec)),some string,$(error "No $(exec) in PATH)))
 
+REVEALHOME=${HOME}/reveal.js
+K := $(if $(shell ls ${REVEALHOME}),some string,$(error "No ${REVEALHOME} found, please execute git clone https://github.com/hakimel/reveal.js)))
+
 DOCMODULES = Sd1 Sda1 Sda2 Tdoc Sdi Persist
 
 doc: