I had missed wrapping one of the checks in ObjectContainer with NDEBUG
which made adding large numbers of particles painfully slow.
I can't submit a patch since it would conflict with the not yet
committed changes. It is simple, the single object insert needs to
have its check wrapped with
IMP_BEGIN_CHECK(EXPENSIVE);
IMP_END_CHECK
And the multipartcle check which is currently CHEAP should be made
EXPENSIVE.