Merge pull request #730 from wenshao/master

add PGExceptionSorter
Merge pull request #731 from wenshao/master

pg sqlparser support drop table if not exists
Merge pull request #732 from wenshao/master

register driver mbean error log level
Merge pull request #733 from wenshao/master

change oracle valid connection impl
improve sqlparser
bugfix for issue 729
Merge pull request #735 from yakolee/master

improve sqlparser & bugfix for issue 729
Merge pull request #736 from wenshao/master

并发优化
Merge pull request #737 from wenshao/master

bug fixed for async closed
Merge pull request #738 from wenshao/master

improved sql parser for sqlserver, support offset fetch clause
Merge pull request #739 from wenshao/master

JdbcUtils support dameng database
JdbcUtils support kingbase