Fix a bug in gclock and clock eviction policies.
Fix a bug in gclock and clock eviction policies.

icoming/FlashGraph,icoming/FlashX,zheng-da/FlashX,icoming/FlashGraph,flashxio/FlashX,silky/FlashGraph,zheng-da/FlashX,flashxio/FlashX,zheng-da/FlashX,flashxio/FlashX,silky/FlashGraph,icoming/FlashX,icoming/FlashX,icoming/FlashGraph,zheng-da/FlashX,flashxio/FlashX,icoming/FlashGraph,flashxio/FlashX,icoming/FlashX,silky/FlashGraph,icoming/FlashX,zheng-da/FlashX,silky/FlashGraph,flashxio/FlashX,silky/FlashGraph,icoming/FlashGraph