Merge pull request #8060 from senny/7313_descriptive_error_message_for_missing_adapter

descriptive error message when AR adapter was not found. Closes #7313
Whitespace :heart: and hash syntax change
Remove XML Parser from ActionDispatch

If you want an ability to parse XML parameters, please install
`actionpack-xml_parser` gem.
Merge pull request #9328 from sikachu/ps-remove-xml-parser

Remove XML Parser from ActionDispatch
make connection_url_to_hash a class method
standardize database_configuration to a hash

This prevents loading database.yml if it doesn't exist but
DATABASE_URL does
test DATABASE_URL without database.yml around
run the load_structure test in the test environment
update changelog