Support for Rails/ActiveRecord 4.1.x

The only real adapter API change was support for CREATE AS SELECT (`as` argument to `create_table_definition`). Implement support for that in `SchemaCreation` but disable tests as we don't yet support it.

The rest of the changes were minor but most related to tests assumptions:
- Slightly more flexible test patching as a single one can't be shared between 4.0 and 4.1
- Use MiniTest directly for our unit tests to avoid conflicting versions
- Consolidate AR version checking into a helper as a few were getting unwieldy
- Refactor log helpers and to ensure we're always logging (or not) the same statements as default adapters
- Clean up the stale prepared statement path via a new (internal only) error class
- Switch back to manually committing around `alter_seq_restart` to avoid blocking on the auto-commit fix

Tests run clean on 3.2.19, 4.0.8 and 4.1.2 (modulo newly logged bugs).