Added an example of propagating CV to i-PI outside of the regtests

examples/features/metadynamics/pimd_metadynamics_zundel/input.xml

@@ -9,11 +9,13 @@
    <ffplumed name="plumed">
          <file mode="xyz">./h5o2+.xyz</file>
          <plumeddat> plumed/plumed.dat </plumeddat>
+         <plumedextras> [doo, co1.lessthan, co2.lessthan, mtd.bias ] </plumedextras>
    </ffplumed>
    <total_steps>400</total_steps>
    <output prefix="data">
       <trajectory stride="40" filename="pos" cell_units="angstrom">positions{angstrom}</trajectory>
       <trajectory stride="20" filename="xc" format="xyz">x_centroid{angstrom}</trajectory>
+      <trajectory stride="20" filename="doo" bead="0" extra_type="doo"> extras_bias </trajectory>
       <properties stride="2"> [ step, time, conserved, temperature{kelvin}, kinetic_cv, 
             potential, kinetic_cv(H), kinetic_cv(O), ensemble_bias ] </properties>
    </output>
@@ -33,7 +35,9 @@
       <ensemble>
          <temperature units="kelvin"> 300.0 </temperature>
          <bias>
-            <force forcefield="plumed" nbeads="1"></force>
+           <force forcefield="plumed" nbeads="1">
+             <force_extras> [ doo, mtd.bias ] </force_extras>
+           </force>
          </bias>
       </ensemble>
       <motion mode="dynamics">

examples/temp/pes/pswater/contract-extras/input.xml

@@ -31,7 +31,7 @@
         <!-- The line below is the one that tells i-PI that the 'dipole' extras quantity will be 
         treated as a physical quantity like forces. It can then be interpolated, and if there are
         several force components, it will be automatically summed with the respective weights -->
-        <force_extras> ['dipole'] </force_extras>
+        <force_extras> [dipole] </force_extras>
       </force>
     </forces>
     <ensemble>