remove @reconnect option on master

it was happening on *every* error, even duplicate keys. the "scheduled"
reconnect afterwards would create a time bomb for whatever transaction
came next, since reconnecting implicitly rolls back transactions.

also, we can let activerecord handle this.
combine send_to_current and send_to_master
remove surprise fallback to master

this was rescuing *any* exception. dangerous. also, no exceptions
are expected from #next anymore.
remove comments that simply repeat the code