Slightly improved compatibility with drivers that only support JDBC 3 API

[fmodesto]

Commit: a154e54
BaseExecutor.closeStatement() invokes statement.isClosed() which is from java 1.6
This crashed with old drivers:

java.lang.AbstractMethodError: Method com/ibm/db2/jcc/am/zo.isClosed()Z is abstract
	at com.ibm.db2.jcc.am.zo.isClosed(Unknown Source) ~[db2jcc-v10.5FixPak06.jcc4.19.26.jar:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_162]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_162]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_162]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_162]
	at org.apache.tomcat.jdbc.pool.StatementFacade$StatementProxy.invoke(StatementFacade.java:114) ~[tomcat-jdbc-8.5.27.jar:na]
	at com.sun.proxy.$Proxy113.isClosed(Unknown Source) ~[na:na]
	at org.apache.ibatis.executor.BaseExecutor.closeStatement(BaseExecutor.java:285) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:65) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:326) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148) ~[mybatis-3.4.6.jar:3.4.6]
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141) ~[mybatis-3.4.6.jar:3.4.6]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_162]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_162]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_162]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_162]
	at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:433) ~[mybatis-spring-1.3.2.jar:1.3.2]
	at com.sun.proxy.$Proxy71.selectList(Unknown Source) ~[na:na]
	at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:230) ~[mybatis-spring-1.3.2.jar:1.3.2]

[harawata]

I was aware [1], but I'll revert the commit as calling isClosed() is not important there.

Note that MyBatis 3.5.0 requires Java 8 which means it does not support such an old driver officially.
And there will be some functionalities that use newer JDBC API.

[1] https://groups.google.com/d/msg/mybatis-user/qYH1oeRTdBU/uwqyXwIeCgAJ