Client lib: fix path cache invalidation and insertion to handle concurrent i-node number changes performed by other simultaneously running QFS client. One such failure was exhibited with listing directory "a" with single directory entry "a", then performing the following sequence from another qfs client: mkdir b; mv a/a b/ ; rmdir a ; mv b a; then listing directory "a" again after 30 seconds (i-node cache invalidation interval) passes. Invalidate cached i-node number entries with path prefix if i-node number changes. Clear cached entries with the common directory prefix before inserting results of read dir plus into the i-node cache, in order to clear stale directory entries, if any, and handle possible change in the directory i-node number.