Patch to use query_timeout in rlm_sql_mysql

[Alan DeKok]

Brian De Wolf wrote:
> The rlm_sql module has a query_timeout option but it wasn't being used
> in the mysql driver.  The attached patch adds the appropriate lines to
> set mysql library options to use timeouts based on query_timeout for
> connecting, reads, and writes.
> 
> The only confusing caveat is that the read and write timeouts
> apparently have retries built-in, so the timeout is effectively 3 times
> the query_timeout time.

  I've added it, with a fix for the 3x retry.

  Alan DeKok.