ii: GRN_II_REDUCE_EXPIRE_ENABLE -> GRN_II_REDUCE_EXPIRE_THRESHOLD
ii: GRN_II_REDUCE_EXPIRE_ENABLE -> GRN_II_REDUCE_EXPIRE_THRESHOLD

GRN_II_REDUCE_EXPIRE_THRESHOLD=0 == GRN_II_REDUCE_EXPIRE_ENABLE=no

GRN_II_REDUCE_EXPIRE_THRESHOLD=-1 (default) uses
ii->chunk->max_map_seg / 2 as threshold.

GRN_II_REDUCE_EXPIRE_THRESHOLD > 0 uses
MIN(ii->chunk->max_map_seg / 2, GRN_II_REDUCE_EXPIRE_THRESHOLD)
as threshold.

kenhys/groonga,cosmo0920/groonga,groonga/groonga,komainu8/groonga,cosmo0920/groonga,komainu8/groonga,kenhys/groonga,cosmo0920/groonga,cosmo0920/groonga,groonga/groonga,cosmo0920/groonga,cosmo0920/groonga,groonga/groonga,naoa/groonga,kenhys/groonga,komainu8/groonga,komainu8/groonga,groonga/groonga,groonga/groonga,cosmo0920/groonga,naoa/groonga,komainu8/groonga,naoa/groonga,kenhys/groonga,groonga/groonga,naoa/groonga,naoa/groonga,komainu8/groonga,kenhys/groonga,naoa/groonga,komainu8/groonga,komainu8/groonga,kenhys/groonga,kenhys/groonga,groonga/groonga,cosmo0920/groonga,groonga/groonga,naoa/groonga,kenhys/groonga,naoa/groonga