EAGLE_12 test reports bad particle drift.

When running the standard EAGLE_12 test configured using:

./configure --enable-debug --enable-debugging-checks --with-metis --disable-vec

with a GCC 5.4.0 compiler, after a large number of steps (seen after 8k) a report like:

 drift.h:drift_part():86: particle has not been drifted to the current time p->ti_drift=28516933577998336, c->ti_old=28508137484976128, ti_current=28516933577998336

is seen.

Originally found when looking at merge request !340 (merged).

Assigning to you @pedro as probably related to !327 (merged).