Objecter: librados: mass switch from eversion_t to version_t

Objecter: librados: mass switch from eversion_t to version_t

There are a lot of pointers throughout our request infrastructure used solely
for exporting the version to users. The interfaces we actually expose only
provide a uint64_t (leaving off eversion_t's epoch), and that's all we're
going to maintain in our new user_version scheme, so don't pretend we'll
have more in our internal interfaces.

I audited this pretty carefully; in particular:
Op::objver is only used for passing data back to users via the calling
functions IoCtxImpl::last_objver, etc
IoCtxImpl::last_objver is used only for the set_sync_op_version() call, which
provides data only for the uint64_t get_last_version() and
rados_get_last_version() calls.
AioCompletionImpl::objver is used only for the uint64_t get_version() call.
LingerOp::pobjver is used only for referencing things that are now version_t.

Signed-off-by: Greg Farnum <greg@inktank.com>