git-svn-id: https://svn.apache.org/repos/asf/maven/maven-1/plugins/trunk@428749 13f79535-47bb-0310-9956-ffa450edef68
We must edit maven-xdoc.dtd in the ${plugin.resources}/dtd directory
but never maven-xdoc-${currentRelease}.dtd in src/dtd.
Every time a new version of the plugin is released, we copy
${plugin.resources}/dtd/maven-xdoc.dtd into
src/dtd/maven-xdoc-${currentRelease}.dtd.
We store maven-xdoc-${currentRelease}.dtd in the SCM to be able
to re-publish them if necessary.