* in collisionsolver.cc: split checkContacts() into a checkContacts() function
  (which only check/update the contacts and returns the number
  of contact constraints) and a getContactsInfo() which only does the
  matrix filling.
* in world.cc:
 - thanks to above change no need to have addContacts/clearContacts
   anymore (this was inefficient)
 - reorder the checkContacts() / getContactsInfo() functions calls
   such that the dimensions of the sparse matrices are set before we
   start filling them.

svn path=/trunk/KDE/kdeedu/step/; revision=927880