b=4778

b=4778
r=dilger

DESCRIPTION:
    oscc->oscc_last_id and filter_last_id will mismatch
after using Lustre for a while, and will trigger LASSERTF.
this patch contains two modification:
    1, the whole operation of deleting orphans or precreating objects is
       protected by filter->fo_create_lock
    2, compare 'conn_cnt' before deleting or precreating, then avoid old
       request to be processed