debian: move ceph-dencoder to ceph from ceph-common

It links against the world currently (notably leveldb).  Not nice for the
client-side lib.

Signed-off-by: Sage Weil <sage@redhat.com>
ceph.spec: move ceph-dencoder to ceph from ceph-common

Signed-off-by: Sage Weil <sage@redhat.com>
configure: do not link leveldb with everything

Detect leveldb, but do not let autoconf blindly link it with everything on the
planet.

Signed-off-by: Dan Mick <dan.mick@inktank.com>
Sighed-off-by: Sage Weil <sage@redhat.com>
Merge pull request #2104 from ceph/wip-dencoder

move ceph-dencoder to ceph from ceph-common

Reviewed-by: Dan Mick <dan.mick@inktank.com>