[mysql] support "disabling" abandoned connection cleanup thread
[mysql] support "disabling" abandoned connection cleanup thread

due leaks on hot re-deploys - will probably be shutdown by default on the next major version or AR-JDBC

jruby/activerecord-jdbc-adapter,keeguon/activerecord-jdbc-adapter,kares/activerecord-jdbc-adapter,kares/activerecord-jdbc-adapter,jruby/activerecord-jdbc-adapter,bruceadams/activerecord-jdbc-adapter,keeguon/activerecord-jdbc-adapter,bruceadams/activerecord-jdbc-adapter,keeguon/activerecord-jdbc-adapter,bruceadams/activerecord-jdbc-adapter,kares/activerecord-jdbc-adapter,jruby/activerecord-jdbc-adapter