[BUGS]log can not be output when use DataSource

Hi,

In the following code,log can not be output as expected.

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org.postgresql.Driver.setLogLevel(org.postgresql.Driver.DEBUG);
DataSource source = (DataSource)new InitialContext().lookup("DataSource");
Connection con = source.getConnection();
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It's seems to be a problem,
I have made a small patch to fix it.
Hopefully this useful.

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Best Regards,
Chen Huajun