Re-entering eviction can result in checkpoint corruption

/*      

 * Eviction cannot free overflow items once a checkpoint is

 * running in a tree: that can corrupt the checkpoint's block

 * management.  Assert that checkpoints aren't running to make 

 * sure we're catching all paths and to avoid regressions.

 */      

WT_ASSERT(session,

    S2BT(session)->checkpointing != WT_CKPT_RUNNING ||

    WT_SESSION_IS_CHECKPOINT(session));