Fix frame update and allow non-parallel

[jamesmkrieger]

Without this fix, we can see on the last pull request that we get the same number of water bridges for groups of frames.

Having the option to not use the parallel code when max_proc=1 is also a good thing to have.

[karolamik13]

Works fine.

waterBridges = calcWaterBridgesTrajectory(coords_traj, trajectory, method='chain')
@> Frame: 0
@> Frame: 1
@> Frame: 2
@> Frame: 3
@> Frame: 4
@> Frame: 5
@> 48 water bridges detected using method chain for frame 0
@> 97 water bridges detected using method chain for frame 1
@> 126 water bridges detected using method chain for frame 3
@> 142 water bridges detected using method chain for frame 2
@> 103 water bridges detected using method chain for frame 5
@> 94 water bridges detected using method chain for frame 4
@> Frame: 6
@> Frame: 7
@> Frame: 8
@> Frame: 9
@> Frame: 10
@> Frame: 11
@> 85 water bridges detected using method chain for frame 6
@> 97 water bridges detected using method chain for frame 8
@> 82 water bridges detected using method chain for frame 7
@> 104 water bridges detected using method chain for frame 11
@> 114 water bridges detected using method chain for frame 9
@> 109 water bridges detected using method chain for frame 10
...

waterBridges2 = calcWaterBridgesTrajectory(coords_traj, trajectory, method='chain', max_proc=1)
@> Frame: 0
@> 48 water bridges detected using method chain for frame 0
@> Frame: 1
@> 97 water bridges detected using method chain for frame 1
@> Frame: 2
@> 142 water bridges detected using method chain for frame 2
@> Frame: 3
@> 126 water bridges detected using method chain for frame 3
@> Frame: 4
@> 94 water bridges detected using method chain for frame 4
@> Frame: 5
@> 103 water bridges detected using method chain for frame 5
@> Frame: 6
@> 85 water bridges detected using method chain for frame 6
@> Frame: 7
@> 82 water bridges detected using method chain for frame 7
@> Frame: 8
@> 97 water bridges detected using method chain for frame 8
@> Frame: 9
@> 114 water bridges detected using method chain for frame 9
@> Frame: 10
@> 109 water bridges detected using method chain for frame 10
@> Frame: 11
@> 104 water bridges detected using method chain for frame 11
@> Frame: 12
@> 102 water bridges detected using method chain for frame 12
@> Frame: 13
@> 103 water bridges detected using method chain for frame 13
@> Frame: 14
@> 112 water bridges detected using method chain for frame 14
@> Frame: 15
@> 101 water bridges detected using method chain for frame 15
@> Frame: 16
@> 92 water bridges detected using method chain for frame 16
...