client: trim deleted inode

Previous patch makes MDS send notification to clients when an inode
is deleted. When receiving a such notification, we invalidate any
dentry link to the deleted inode. If there is no other reference to
the inode, the inode gets trimmed.

For cephfs fuse client, we use fuse_lowlevel_notify_inval_entry() or
fuse_lowlevel_notify_delete() to notify the kernel to trim the deleted
inode. (this is not completely reliable because we play unlink/link
tricks when  handle MDS replies. it's difficult to keep the user space
cache and kernel dcache in sync)

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
ceph: Update FUSE_USE_VERSION from 26 to 30.

When compiling, it met this error:
>In file included from /usr/local/include/fuse/fuse.h:19:0,
>                 from client/fuse_ll.cc:17:
>/usr/local/include/fuse/fuse_common.h:474:4: error: #error only API
>version 30 or greater is supported
Update FUSE_USE_VERSION from 26 to 30.

Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>