Plugins with indirect dependency on plexus-utils are stuck with plexus-utils:1.1

To compensate the effect that MNG-2892 would have on bad plugins, a hack was put into the core that automagically injects plexus-utils:1.1 as a direct plugin dependency if the plugin does not already declare a direct dependency on plexus-utils:1.1+. However, only checking the plugin's direct dependencies for plexus-utils ignores any version of plexus-utils that is used by a transitive dependency. This corrupts the runtime class path of the plugin and can result in linkage errors like reported in AW: NPE with maven-changelog-plugin and git.