grn_obj_remove(): reduce the max memory usage
grn_obj_remove(): reduce the max memory usage

If grn_thread_get_limit() returns 1, grn_obj_remove() closes temporary
opened objects that are not opened before grn_obj_remove() is called.

komainu8/groonga,groonga/groonga,naoa/groonga,groonga/groonga,hiroyuki-sato/groonga,cosmo0920/groonga,naoa/groonga,kenhys/groonga,cosmo0920/groonga,naoa/groonga,hiroyuki-sato/groonga,cosmo0920/groonga,hiroyuki-sato/groonga,komainu8/groonga,groonga/groonga,kenhys/groonga,komainu8/groonga,hiroyuki-sato/groonga,komainu8/groonga,groonga/groonga,hiroyuki-sato/groonga,naoa/groonga,cosmo0920/groonga,groonga/groonga,kenhys/groonga,kenhys/groonga,cosmo0920/groonga,groonga/groonga,komainu8/groonga,groonga/groonga,naoa/groonga,kenhys/groonga,komainu8/groonga,hiroyuki-sato/groonga,hiroyuki-sato/groonga,naoa/groonga,kenhys/groonga,groonga/groonga,kenhys/groonga,hiroyuki-sato/groonga,cosmo0920/groonga,komainu8/groonga,cosmo0920/groonga,cosmo0920/groonga,naoa/groonga,naoa/groonga,komainu8/groonga,kenhys/groonga