Fix panic when comparing unequal maps.

The change in #94 resulted in using == to compare two values that might not be
comparable. Hence, this resulted in a panic for situations like:

    ObjectsAreEqual(map[int]int{5: 10}, map[int]int{10: 20})

The fix is to use reflect.DeepEqual() instead.
fix merge conflict
Merge branch 'neilconway-map-non-equal-panic'