new column convention and adapter tests for PostgreSQL/MySQL
allow to specify caller depth with deprecate
add a "WARNING: " prefix for all the warning messages ArJdbc generates
test raw JdbcAdapter passed an instantiated (jdbc) connection
[mysql] `variables: false` (with `encoding: false`) config to stub configure_connection
[mysql] no longer default to config[:encoding] = 'utf8' (and *useUnicode = true*)
... the (official) Connector/J driver shall auto-detect and use those correctly
[mysql] when config[:encoding] set with official driver - avoid SET NAMES ... statement