Parallel MDFF cross-correlation calcuation
Example run:
vmd -dispdev text -e  call-crosscorr-dyn-defsel.vmd -args sim.psf sim.dcd density.dx struct-fixes-if-needed.tcl selction-definitions.list 0 10000 6.5 -999 0 -999 0 2 3000 sim-crosscorr.tml > sim-crosscorr.log

See call-crosscorr-dyn-defsel.vmd for parameter list
