Remove merb/webrat integration

Merb has been dead for over three years.  This support was never
documented, and didn't include the transactional testing
supported by the other test integration modules.
Add support for rspec 2+ to the rspec/sequel integration

Previously, the code only worked with rspec 1.

Add specs that test the rspec/sequel integration, and
add support for fixture_dependencies itself to work
with rspec 2+.

Use the :rollback=>:always transaction option instead
of manually raising Sequel::Rollback for transactional
handling.

Bump copyright year as well.
Bump version to 1.3.3