common/TrackedOp: use explicit ref count, intrusive_ptr

common/TrackedOp: use explicit ref count, intrusive_ptr

This is more efficient and more explicit than shared_ptr.  It will also
allow us to put these in intrusive lists.

Note that before we used the shared_ptr OnDelete property only for the
live ops and left it off for the history.  Here we rename is_tracked to
state and explicit note whether we are untracked, live, or history.

Also, now that we #include OpRequest in osd_types.h, we have to include
the .cc file (and ~OpRequest definition) in libcommon to avoid a link
error on all the unit tests etc.

Signed-off-by: Sage Weil <sage@redhat.com>