[COOT] Request: Symmetry atoms should update dynamically (or with option)

[Ezra Peisach]

Howdy,

Today I found too atoms close together - and realized they were one and 
the same - close to a special position - the other being the symmetry 
mate.  I moved one atom (move/translate zone) - but the other did not 
move until I went to another atom and came back. It would be nice if 
when moving the first atom - the symmetry related one moved to - it 
would have made centering on the special position easier.

I know this might be computationally expensive - so have a preference to 
turn it on or off.

Ezra