Update gaerdbms to highlight improved connection method

(cherry picked from commit 0d15791a6e3ec35e3c2e297026d8396742e30a34)
- make the google deprecation messages more specific, use full URL
format
- add an extra doc to MySQLdb
- changelog

(cherry picked from commit 182553b7409cfa6673483d03f29bc4c462336577)