********> bugfix.9
Author:   Bill Ross
Date:     11/23/97

Programs: xleap

Severity: crash

Description:

	xleap crashes, often in addIons, because of an error in the
	graphics update code: if there is a single object on the
	update queue, and this object is immediately added again,
	the queue is corrupted. This happens when copying a single-atom 
	residue such as a monoatomic ion: the "head" and "tail" point 
	to the same atom, and this atom is added to the queue twice.

Workaround:

	Use tleap for operations that crash xleap.

Fix:	Make the following change to displayer.c:
-------------------------------------------------------------------------

*** OLD displayer.c
--- NEW displayer.c
***************
*** 269,278
  		/* accumulate the updates then accumulate and continue */
  
      if ( GiDisplayerAccumulateUpdates != 0 ) {
!     	if ( dDisp->dNext == NULL ) {
! 	    dDisp->dNext = SdDisplayerAccumulateList;
! 	    SdDisplayerAccumulateList = dDisp;
! 	}
  	RETURNV;
      }
  		/* If the DISPLAYER is insensitive then */

--- 269,282 -----
  		/* accumulate the updates then accumulate and continue */
  
      if ( GiDisplayerAccumulateUpdates != 0 ) {
! 	DISPLAYER	dTmp;
! 	for (dTmp=SdDisplayerAccumulateList; dTmp; dTmp=dTmp->dNext)
! 		if ( dTmp == dDisp )
! 			RETURNV;
!     	if ( dDisp->dNext != NULL )
! 		DFATAL(("bad dDisp->dNext pointer\n"));
! 	dDisp->dNext = SdDisplayerAccumulateList;
! 	SdDisplayerAccumulateList = dDisp;
  	RETURNV;
      }
  		/* If the DISPLAYER is insensitive then */
-------------------------------------------------------------------------