Unserialize ll_open.

Includes update to trim_cache, threading cf argument.  In part,
completes the prior commit, since ll_create can at least
apparently call _open.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Pass CF_ILOCKED to _create_fh.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>
Unserialize ll_mkdir, mkdir, _mkdir.

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