Several improvements regarding version handling:
* Allow DB#version_tuple to work even if mysqld is stopped.
* Add DB#normalized_version to get the version as a string, with a specified
  amount of precision.
* jetpants_collins: Add an overrideable hook, process_spare_selector_options,
  that can interpret nonstandard options passed to claim_spares or
  count_spares. Initial proposed use would be for a :version param, to obtain
  spares with a specific version of mysql installed.