In fcoll_two_phase_supprot_fns.c: calculation of the aggregator index
failed for large offsets on 32bit machine, due to improper handling of
64bit offsets.
Fixes Issue #7110
Signed-off-by: Edgar Gabriel <egabriel@central.uh.edu>
(cherry picked from commit ea1355beae918b3acd67d5c0ccc44afbcc5b7ca9)