b=15692 statahead should hold parent dir's i_mutex to synchronize with other operatio...

b=15692 statahead should hold parent dir's i_mutex to synchronize with other operations from VFS layer when inserting dentry to dcache

1) statahead should hold parent dir's i_mutex to synchronize with other operations from VFS layer when inserting dentry to dcache
2) drop unused ll_lookup_lock
3) drop unused DCACHE_LUSTRE_INVALID definition checking
4) more debug information
5) other code cleanup

i=robert.read
i=eric.mei