This relates to commit 4eb08a58 that was applied to pair_dpd_fdt_energy

This saves around 10% of the runtime for many of our tests using SSA.

1) Added MY_EPSILON to handle machine precision checks
2) Removed error checks for DPD-RX; enabled use with DPD-E simulations
3) Expanded the EOS functional form to allow corrections
   in the thermo file or on the command line
4) Updated naming convention from fraction to mixWtSite*
5) Changed the name of getParams() method to getMixingWeights()
6) getMixingWeights() now handles fractional and molecular weighting
7) Added optional argument (fractional or molecular) to pair_style command
8) Added argument to specify the exp6 parameter scaling method
   NOTE: Requires additional arguments in the pair coefficients,
   thus command line areguments are NOT backward-compatible.

This makes our results more closely match a vetted serial implementation.
NOTE: This does make the output different from any previous versions.
Patch by Jim Larentzos.  Applied by Tim Mattox.

Patch by Jim Larentzos.  Applied by Tim Mattox.

Patch by Jim Larentzos.  Applied by Tim Mattox.

pair_exp6_rx.cpp patch by Jim Larentzos.  Applied by Tim Mattox.

instead of having pair_dpd_fdt* make the SSA-neighbor list request for it.
Forces an "extra" list to be built, but now skip lists work properly.
Maybe we can detect if skip lists won't be used, and squash the extra list.

Move the calculation of dtsqrt inside FixShardlow::initial_integrate()

Includes documentation and examples.
NOTE: VV requires very small timesteps under isoenergetic conditions.
Consider using fix_shardlow instead, since this VV support is
primarily for comparison purposes.

Removes most SSA specific fields from class NeighList.

git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@15355 f3b2605a-c512-4ea7-a41b-209d697bcdaa