make gradle eclipse always run cleanEclipse

Otherwise the 'merging' gets really trappy. it basically never works without a clean.

See 38.4.1.1. Disabling merging with a complete rewrite:
https://docs.gradle.org/current/userguide/eclipse_plugin.html

build.gradle

@@ -158,6 +158,8 @@ allprojects {
       defaultOutputDir = new File(project.buildDir, 'eclipse')
     }
   }
+  // otherwise the eclipse merging is *super confusing*
+  tasks.eclipse.dependsOn(cleanEclipse)
 }
 
 idea {