According to
<http://dev.mysql.com/doc/refman/5.5/en/c-api-threaded-clients.html>,
(potentially) threaded clients should use the reentrant
libmysqlclient_r.  This is just a precaution, I haven't seen any
issues with the normal libmysqlclient.

Change-Id: Icb29df6dd54eb666e3b43b73fbda406acccd11cb