Add disabled test for renaming directories.

problems.

This prevents "Failed to clone namespace" problem on some platforms.

syscall.Umount() does not update /etc/mtab.

Drop sleep statements for unmount tests.

This can be used to advise the kernel of updated attributes or data of
existing data; it cannot be used to remove negative entries.

Don't run TestAccess for root.

For 32 bit platforms, we don't want to generate 64 bit inode numbers,
as that will cause EOVERFLOW when running stat() and friends.

DESTROY is only sent for fuseblk devices which we (probably) don't
support anyway.

Previously, a FORGET opcode could force a mount that was unused to be
forgotten.  This would cause the mounting filesystem to get into
inconsistent states: MultiZipFs and AutoUnionFs would believe the
mount is still live, but FilesystemConnector had already forgotten it.

The downside to this solution is that submount FileSystems will no
longer be unmounted if the root FileSystem is unmounted with
"fusermount -u".

Add a gotest benchmark running off a synthetic stat-only filesystem.

mount point.

Test for behavior of deletion cache drop too.