This fixes a fascinating segfault. This is the sequence of events:

This fixes a fascinating segfault.  This is the sequence of events:
1) A restart occurs
2) A shared term is registered to arithmetic.
3) Arithmetic sets this up.
4) No new linear relations are added to arithmetic.
5) Eventually a restart occurs.
6) Arithmetic resets the tableau as it has not had a row added since the last restart.
7) A new variable is added.
8) This exceeds the size of the column vector of the saved tableau by exactly one.
9) segfault