[gmx-revision] Changed PME spacing for triclinic cells

[Erik Lindahl]

PME grid dimensions are now calculated from spacing along (non- 
orthogonal) triclinic box vectors rather than orthogonal cartesian  
distances. This improves the accuracy of free energy calculations  
with pme_order=4.

Note that the grid calculation occurs in grompp, so you will need to  
regenerate the tpr files for it to have effect.

Cheers,

Erik