Anyway, I couldn't set anything with the URL or the init-params. I just
added a breakpoint and manually changed "traceProtocol" and
"detectServerPreparedStmts" (aka "useServerPrepStmts") to true. Voila!
Things again work as expected.
Whoops. I meant that I set "detectServerPreparedStmts" to false.
Okay, I finally found a way to reproduce it with the command line
client, so this bug has nothing to do with Connector/J; however, the bit
about Resin might be useful to anyone using it via
ConnectionPoolDataSource or MysqlXADataSource.