This keeps the begin migration/end migrations lines lined up nicely.
…rning user if they haven't set options[:atomic_switch] and they have an affected version of mysql. Default to true for good versions.
with mysql2 (by not using fetch_row)
…destination tables 2) adds option[:atomic_switch] boolean to specify use of AtomicSwitch or LockedSwitcher 3) warn user if options[:atomic_switch] is not set & their version is affected by old mysql bug, and default options[:atomic_switch] to false