Added -range option to cell.plt and econste_cmp.plt

util/cell.plt

 #!/bin/bash
 # cell.plt: plot cell parameters during an MD simulation
+if [ $1 == "-range" ]
+then
+  range=$2
+  shift 2
+fi
+
 gnuplot -persist <<EOF
-plot "<grep -h -A3 '<unit_cell' $* | grep a=" u 2 w l, \
+plot $range "<grep -h -A3 '<unit_cell' $* | grep a=" u 2 w l, \
      "<grep -h -A3 '<unit_cell' $* | grep a=" u 3 w l, \
      "<grep -h -A3 '<unit_cell' $* | grep a=" u 4 w l, \
      "<grep -h -A3 '<unit_cell' $* | grep b=" u 2 w l, \

util/econste_cmp.plt

 #!/bin/bash
 # econste_cmp.plt: compare <econst> and <etotal> in two MD simulations
 # use: econste_cmp.plt mdrun1.r mdrun2.r
+if [ $1 == "-range" ]
+then
+  range=$2
+  shift 2
+fi
 gnuplot -persist <<EOF
-p "<grep -h econst $1" u 2 w l, "<grep -h '<etotal>' $1" u 2 w l, \
+p $range "<grep -h econst $1" u 2 w l, "<grep -h '<etotal>' $1" u 2 w l, \
   "<grep -h econst $2" u 2 w l, "<grep -h '<etotal>' $2" u 2 w l
 
 EOF