Made print_secondary not take a default value for tag_num.
Added and made use of type reql_version_t, instead of using cluster_version_t for reql versions.

(Very soon we might be passing reql versions over the cluster, and it would
be weird to be sending cluster_version_t values.)
Made print_secondary and its extractors take a reql version, passed up the reql version everywhere except to sindex_readgen_t.
Added the sindex_reql_version field to rget_read_response_t, but right now nothing uses it.
Made sindex_reql_version be initialized.
Made sindex_readgen_t::sindex_sort_read actually use the true secondary index reql version... barring bugs.
Merge branch 'grey_binary_sindex' into sam_2789_keyfix
Made datum_t::cmp and print_secondary be properly reql-versioned, but passed in reql_version_t::RSI everywhere.
Made predicate_term_t::pred be a plain reql_version_t-taking func.
Made leq and geq datum_t reql predicates be versioned.
Replaced datum_t::operator> with a versioned compare_gt.
Used explicit operator bool for counted_t, thank you C++11.
Removed counted_t::operator<, used counted_datum_less_t.
Removed the thankfully unused scoped_ptr_t::operator<.
Replaced datum_t::operator< with versioned compare_lt.
Made datum_lt and datum_gt in shards.cc receive actual env_t reql_version.
Used env reql_version in orderby_term_t.
Made between_term_t use env reql_version.
Made counted_datum_less_t take a reql_version_t.
Made rget_cb_t::handle_pair use the env reql_version in its groups_t.