IVY-1662: collect updates by conf and check transitive on old dependency

[eric-milles]

The ivy:checkdepsupdate task should examine dependencies by conf so that it does not report on a dependency in another conf that has an update. For example, if org.dom4j:dom4j:2.2.0 is in "conf1" and com.github.spotbugs:spotbugs-ant:4.9.3 is in "conf2" there is a transitive dependency to org.dom4j:dom4j:2.1.4. With <ivy:checkdepsupdate conf="conf1" revisionToCheck="latest.release" showTransitive="false" /> there is a line "org.dom4j#dom4j 2.1.4 -> 2.2.0".

https://issues.apache.org/jira/browse/IVY-1662