Proposed adjustments to LL v2 API:

Integration of existing components, particularly FUSE, suggests that
we should preserve support for OPEN and CREATE returning file handles,
while still adding inode variants.

In this version, the Client::ll_* interface contains just expanded
signatures for the base methods.  If a filehandle pointer is provided,
the underlying call path does the right thing.  A new ll_close variant with
mode mask is added to support cleanup of opens with inode handle only.

Finally, Ceph ll_read and ll_write methods already do positional i/o.  Add
placeholders for vector versions of inode i/o operation methods.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Adapt SyntheticClient for adjusted LL V2.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Adapt FUSE client for adjusted LL V2.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>