IsOverlapping return simplified.

I'm not going to include the full proof, but consider the following cases (in pairs of array memory locations):

```
    [  ]
[  ]

   [  ]
[  ]

  [  ]
[  ]

[  ]
[  ]

[  ]
  [  ]

[  ]
   [  ]

[  ]
    [  ]

  [  ]
[      ]

[      ]
  [  ]

[    ]
[  ]

[  ]
[    ]

[    ]
  [  ]

  [  ]
[    ]

```

I don't think there are any more cases.
Merge pull request #2 from Y-Less/master

IsOverlapping return simplified.