GitLab

Converted the array containing atom block indices for the neighbor list from ushort2 to int.  This removes the hard limit of 2 million atoms.

Fixes a hard to catch bug when a boundingBoxSize increases in size in between a timestep, but does not trigger a rebuild of the neighbourlist. Affects the usage of singlePeriodicCopy in nonbonded force.  

When converting to fixed point, multiply by 0x100000000 instead of 0xFFFFFFFF.  This should be (very very slightly) more accurate, since its reciprocal can be exactly represented in floating point.

On Fermi, store forces as 64 bit fixed point and update with atomic operations.  Also various other minor optimizations.

Reduced number of force buffers to one per work group.  Increased work group size for nonbonded interactions.