[mssql] refactored date/time handling (with micro-second precision)
mssql's driver does support savepoints
re-think our AREL support - esp. visitor resolution - simpler & more reliable
some minor drying with MSSQL adapter's LimitHelper
FireBird goes by name Firebird + minor doc/comment tweaks + version++
assert correct visitor type used for (every) adapter
review gemspec/Gemfile deps