Fixed tracking issues

Tracking issues fixed as of commit 678e223385097627453c1d19caa53c201f5bb2b3 fixed issues related to the G1 routines giving the correct answer.

See #71 for the first set of test cases, also performed was testing in a spherical geometry. A spherical geometry containing 3 nested spheres of radii 10,20 and 30 cm were placed inside a hollow box of inner dimensions 100 and thickness 5. In vacuum we scored the track length flux in volumes 1 , 2 and 3 which correspond to the spheres of radii 10,20 and 30 cm.  An isotropic point source was placed at the centre of the 10 cm sphere and all the volumes were assigned the material vacuum. Under these conditions we expect each score to report the average track length being the thickness of the volume, i.e. the result for each volume should be 10 cm.

|Volume # |   Fluka     |   FluDAG |
|:-------------:|:-------------:|:-------------:|
    1    |   9.999996  |   9.999209
    2    |   9.999996  |   10.00000
    3    |   9.999996  |   9.999995

This test is considered passed.

Replacing the vacuum materials, with iron, water and tungsten, respectively we can report the following results for the spectra in volumes 1, 2 and 3

![screenshot from 2013-05-15 22 52 21](https://f.cloud.github.com/assets/2439754/510559/21c82f36-bddc-11e2-8efa-865d3b831867.png)
Volume 1

![screenshot from 2013-05-15 22 52 36](https://f.cloud.github.com/assets/2439754/510560/25f8ef32-bddc-11e2-8652-0663ec8d3287.png)
Volume 2

![screenshot from 2013-05-15 22 52 55](https://f.cloud.github.com/assets/2439754/510561/2a3a3ba0-bddc-11e2-92f2-fa6a1f367967.png)
Volume 3

The total fluxes are

|Volume # |   Fluka     |   FluDAG |
|:-------------:|:-------------:|:-------------:|
    1    |   22.14079  |   22.16578
    2    |   41.58068  |   41.54507
    3    |   11.95607  |   11.88404

Given the evidence in issue #71 and here I consider this issue, at least temporarily closed and certainly that we are getting the correct answer for neutral particles. We should extend testing to charged particles soon.