Patch to improve threadsafeness in the mysql plugins.

NEWS

src/database/mysql_common.c

src/database/mysql_common.h

...ugins/accounting_storage/mysql/accounting_storage_mysql.c

...ugins/accounting_storage/mysql/accounting_storage_mysql.h

src/plugins/accounting_storage/mysql/as_mysql_acct.c

src/plugins/accounting_storage/mysql/as_mysql_archive.c

src/plugins/accounting_storage/mysql/as_mysql_assoc.c

src/plugins/accounting_storage/mysql/as_mysql_cluster.c

src/plugins/accounting_storage/mysql/as_mysql_convert.c

src/plugins/accounting_storage/mysql/as_mysql_convert.h

src/plugins/accounting_storage/mysql/as_mysql_job.c

...ugins/accounting_storage/mysql/as_mysql_jobacct_process.c

src/plugins/accounting_storage/mysql/as_mysql_problems.c

src/plugins/accounting_storage/mysql/as_mysql_qos.c

src/plugins/accounting_storage/mysql/as_mysql_resv.c

src/plugins/accounting_storage/mysql/as_mysql_rollup.c

src/plugins/accounting_storage/mysql/as_mysql_txn.c

src/plugins/accounting_storage/mysql/as_mysql_usage.c

src/plugins/accounting_storage/mysql/as_mysql_user.c