Explain in more detail how we work with branches when creating a new release.

git-svn-id: https://svn.apache.org/repos/asf/ant/ivy/core/trunk@1577380 13f79535-47bb-0310-9956-ffa450edef68
2.4 is also allowed as version in ivy.xml files

git-svn-id: https://svn.apache.org/repos/asf/ant/ivy/core/trunk@1577382 13f79535-47bb-0310-9956-ffa450edef68