Update gemspec to remove `oracle_enhanced.rake`
use `string[-1,1]` for consistency + avoid unnecesary map-ing over an array

Conflicts:

	lib/active_record/connection_adapters/oracle_enhanced_structure_dump.rb
Add entries for oracle_enhanced_database_tasks_spec.rb
Add spec
Move Database Task registration so it can be loaded by test environment and not just rake tasks
ActiveRecord expects config hash to have string keys