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>
(cherry picked from commit b37e3bde3bd31287b11c069062280258666df7c5)
ceph.spec: move ceph-dencoder to ceph from ceph-common

Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit 95f5a448b52db545a2b9bbad47fdb287254f93ea)
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>
(cherry picked from commit 06a8f7b99c5533f397b34f448138220384df60ac)