simulation based on an XPLOR backend. 

constructor:

  XplorSimulation(clone=False):

      create a new xplor process and associated XplorSimulation object. If
   the optional clone argument is True, the current atomic coordinates and
   PSF information are mirrored in the new object. Otherwise, the object
   will have no atoms or PSF information.

Methods:

  This objects contains all of the methods of the <m simulation>.Simulation 
class. In addition, it contains the following:

  potList() - return the <m potList>.PotList of potential terms which are 
              evaluated when the SCRIpting XPLOR energy term is active.


  scriptingIndex() - index into XPLOR renr array corresponding to 
                     SCRIpting term.

  wrap()    - return the associated <m xplorWrap>.XplorWrap object. This 
              member is not usually needed.


  
 The following routines synchronize simulation values to/from xplor. They
are not usually needed.  

  initFrom()          - initialize quantities from XPLOR
  syncFrom()
  syncAtomIDFrom()
  syncPosFrom()
  syncVelFrom()
  syncFricFrom()
  syncChargeFrom()
  syncMassFrom()
  syncTo()            - copy modified coordinates, etc. variables to xplor