Bug fixed 7/15 FG2.31: in Hide, center visible was not working because it uses reDisplay which
changes what is visible prior to centerVisibleSpt. I added two lines,
one each in in reDisplay() (jcontrol.js) and centerVisible()
using ~holdvis to restore the initially visible status prior to centerVisibleSpt.

Bug fixed 6/15 FG2.3: selectionhalos are visible for 'center visible'.
Therefore turned them temporarily off in centerVisibleSpt.

centerVisibleSpt (scripts.js):

// atoms with halos are 'visible' so need to turn off halos before centering.
var centerVisibleSpt =
"isosurface gm* delete;\n\                                                                         
~holdhalos = selectionhalos;\n\                                                                    
selectionhalos false;\n\                                                                           
zoomTo 1.0 {visible};\n\                                                                           
selectionhalos @~holdhalos;\n"; // smooth 1.0 sec                                                  
// Often used after something is hidden. Don't want stray gapmeshes                                
// dragged along hence delete gm*.

centerVisible() is used only in the Hide dialog (help.js).
centerVisible() in jcontrol.js simply does
	reDisplay(makeEchoSpt(VisibleCentered_txt), centerVisibleSpt);

reDisplay() in jcontrol.js is complicated.

centerSpt does 'set picking center' for the Center Atom dialog.

