client: fix use-after-free on session close and cond signals

Move the signal into the closed method, before we deallocate the
MetaSession, so that other callers catch it too.

Signed-off-by: Sage Weil <sage@inktank.com>
client: do sync read when 'client oc = false'

Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #178 from ceph/wip-client

Fix client with cache disabled, and a use-after-free

Reviewed-by: Sam Lang <sam.lang@inktank.com>