Sqoop Export Upsert for MySQL lacks batch support

MySQL export upserts are limited to one row per statement. This wastes bandwidth and makes the exports unusably slow.

I wrote a patch to support multiple rows per statement at (https://github.com/cloudera/sqoop/pull/22/files). Now the records.per.statement parameter actually works, and I get fast exports (60k rows/sec) with 1000 records per statement, 10 statements per transactions, and 5 mappers.