invalid write in engine_addlink
Valgrind throws invalid write errors for engine_addlink. It looks like the allocation in
engine.c:976 if ( ( e->links = malloc( sizeof(struct link) * s->tot_cells * 27 * 2 ) ) == NULL )
does not allocate enough memory...
Increasing the size of the allocation fixes a strange crash when using the glass_001 initial conditions. Since I don't know what the 2 and 27 are, I'll just leave this here.