Minor modification to cmfd.xml's tally_reset_interval logics
Minor modification to cmfd.xml's tally_reset_interval logics

When only one value is entered at tally_reset_interval, this value
is treated as the interval to reset CMFD tallies. It used to be
reset starts at cmfd_begin + interval; this caused trouble in that
the early batches (e.g., cmfd_begin, ... cmfd_begin + interval - 1)
were not reset. This commit starts resetting tallies at the first
accelerated batch when only one value is entered.

lilulu/openmc,lilulu/openmc,lilulu/openmc