When launching JUnit Tests on a package, all Tests contained inside that
package (And nested packages) were launched.
However, Tests contained in sibling packages, that share the same
prefix, were also launched.
com
|
\-- example
   |
   \-- a  <-- Launching JUnit Tests on this package
   |  |
   |  \-- nested
   |  |  |
   |  |  \-- MyNestedTest.java
   |  |
   |  \-- MyTest.java
   |  |
   |  \-- MyOtherTest.java
   |
   \-- ab
      |
      \-- MyTestInSiblingPackage.java <-- Was also executed

Now, only Tests contained in the target package, as well as Tests
contained in real child packages are launched.
Tests contained in sibling packages are no longer considered.